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Rev. Biol. Trop. (Int. J. Trop. Biol.) • Vol. 69(1): 113-126, March 2021

Drivers of diversity and altitudinal distribution of chironomids

(Diptera: Chironomidae) in the Ecuadorian Andes

Christian Villamarín

*, Santiago Villamarín-Cortez

2,3

, Danielle M. Salcido

Mauricio Herrera-Madrid

& Blanca Ríos-Touma

1. Grupo de Investigación BIOMAS, Facultad de Ingenierías y Ciencias Aplicadas, Universidad de Las Américas,

C/ José Queri, Quito, Ecuador; christian.villamarin@udla.edu.ec, blanca.rios@udla.edu.ec

2. Department of Biology, PhD Program in Ecology, Evolution and Conservation, University of Nevada, Reno, Nevada,

United States of America; sanbiol@gmail.com, danisalcido@gmail.com

3. Instituto Nacional de Biodiversidad (INABIO), Rumipamba 341 y Av. Shyris, Quito, Ecuador;

mauricio.herrera@biodiversidad.gob.ec

* Correspondence.

Received 03-III-2020. Corrected 15-X-2020. Accepted 04-XI-2020.

ABSTRACT. Introduction: Chironomids (Diptera: Chironomidae) are the most globally diverse and widely

distributed aquatic insects. Despite their prevalence in lotic systems, little is known about the ecology and

diversity of tropical species relative to other aquatic insect taxa, particularly at the immature stages. Objective:

Characterize chironomid diversity across an elevational gradient in Southwestern Ecuador and water quality

parameters associated with their composition. Methods: Samples were collected using a Surber net in forty riv-

ers within four watersheds in the Ecuadorian Andes comprised of montane and dry lowland forest and spanning

an elevational gradient of 3 120 m.a.s.l. Various physic chemical variables were measured including oxygen,

conductivity, total dissolved solids, temperature, and pH. Results: Generally, environmental variables were

strongly correlated with the composition of chironomid communities. Variation in the chriomid communities

was most strongly associated with oxygen, conductivity and pH. The presence of Parametriocnemus, Cricotopus

f4, Cricotopus sp3., Cricotopus (Isocladius), Oliveiriella, Onconeura, Alotanypus and Pentaneura was associ-

ated with lower temperatures, high dissolved oxygen and low conductivity while assemblages of Cricotopus sp.,

Rheotanytarsus, Tanytarsus, and Chironomus were associated with high conductivity and low concentrations

of dissolved oxygen. The RELATE analysis showed that local environmental characteristics are determine the

composition of the chironomid community. Conclusions: Similarity among local environmental factors was

strongly correlated to similarity among Chironomidae assemblages, especially with variables such as oxygen

concentration, pH and conductivity, whose variables are highly correlated to land use and dominant vegetation

in the watersheds sampled.

Key words: Tropical Andes; environmental variables; diversity patterns.

Chironomidae is one of the most widely

distributed families of aquatic Diptera span-

ning broad latitudinal, altitudinal, and dis-

turbance gradients (Ashe, Murray, & Reiss,

1987). Species within this group are able to

survive a suite of extreme conditions including

freezing temperatures, saline-rich or oxygen-

poor waters. Extraordinary examples include

species that inhabit extreme freezing, hypoxic

or saline environments such as Antarctica,

swamps, brackish water and sewers (Lencioni,

Cranston, & Makarchenko, 2018) via a suite

Villamarín, C., Villamarín-Cortez, S., Salcido, D.M., Herrera-Madrid, M., & Ríos-Touma,

B. (2021). Drivers of diversity and altitudinal distribution of chironomids (Diptera:

Chironomidae) in the Ecuadorian Andes. Revista de Biología Tropical, 69(1), 113-

126. DOI 10.15517/rbt.v69i1.40964

ISSN Printed: 0034-7744 ISSN digital: 2215-2075

DOI 10.15517/rbt.v69i1.40964

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Rev. Biol. Trop. (Int. J. Trop. Biol.) • Vol. 69(1): 113-126, March 2021

of protein adaptations such as hemoglobin-

like respiratory proteins or heat shock proteins

(Hanson, Springer, & Ramirez, 2010). Both

the immature and adult stages of their life-

cycle, make this group extremely important to

aquatic food webs as sources of proteins, lipids

and minerals for fish, amphibians, birds and

other macroinvertebrates (Armitage, Cranston,

& Pinder, 1995).

While these familiar examples highlight

taxa capable of living in extreme environments,

the majority of species have specific habitat

requirements (Lencioni et al., 2018). Species

are sensitive to subtle changes in water quality

and serve as indicators of stream health in fresh-

water biomonitoring assessments (Paggi, 2003).

In addition, individual-level morphological fea-

tures such as teeth deformities can indicate spe-

cific water contaminates (Roback & Coffman,

1983; Ossa et al., 2018). Pollution from mining

and agriculture have altered the physical, chem-

ical and biotic environment of aquatic systems,

especially in the Neo-tropics (Villamarín, Prat,

& Rieradevall, 2014). These result in changes

to nutrient and sedimentation inputs, flow rate,

thermal environment and biotic introductions

(Ríos-Touma & Ramírez, 2019) with implica-

tions for the macroinvertebrate communities

and functional diversity (Prat, Ríos-Touma,

Acosta, & Rieradevall, 2009).

In Ecuador, most Chironomidae research

focuses on systematics and for the subset that

address ecology, identifications are resolved to

family-level morphotypes (Ríos-Touma, Acos-

ta, & Prat, 2014; Encalada et al., 2019). Given

the importance and diversity of this family in

aquatic environments, it is critical to advance

the knowledge with species-level resolution in

an ecological context to understand how envi-

ronmental stressors modify these communities.

Previous studies in the Andean ranges focus on

Northern (Oviedo-Machado & Reinoso-Flórez,

2018) and Central Andes (Acosta & Prat,

2010) and have shown differences in subfamily

composition across elevational cline. Domi-

nant subfamilies at higher elevations include

Orthocladiinae, Podonominae and Diamesi-

nae, while lower elevations Chironominae and

Tanypodinae dominate indicating the role of

elevation, temperature and stream physical

characteristics in structuring these communi-

ties (Acosta & Prat, 2010; Oviedo-Machado &

Reinoso-Flórez, 2018).

Southern Ecuador exhibits exceptional

endemism (Mittermeier, Myers, Thomsen, da

Fonseca, & Olivieri, 1998) and is a biodiver-

sity hotspot (Mittermeier et al., 1998) in part

because of the several unique ecoregions, prox-

imity to arid and semi-arid areas of Northern

Perú (Sierra, 1999) and the Andean depression

(also known as the Depression of Huanca-

bamba) a valley separating the central Andes

from the Northern (Villamarín, Rieradevall,

& Prat, 2020). Despite the extreme ende-

mism of this region, studies characterizing

aquatic macroinvertebrate fauna, particularly

among Chrironomidae, are scarce. Understand-

ing environmental factors shaping chironomid

diversity is particularly important as rivers in

the region are continually impacted by land-use

change (Ríos-Touma & Ramírez, 2019). Here

we analyze how elevation and environmental

gradients shape the Chironomid community

composition in four watersheds of Southwest-

ern Ecuador to understand the environmen-

tal drivers of the diversity of this important

aquatic group.

MATERIALS AND METHODS

Study Area: The study took place at El

Oro Province, in Southwestern Ecuador. This

region has marked seasonality, a dry season

(June-October) and wet season (December-

May) (Escribano-Ávila, 2016). The samples

were taken only in dry season to minimize the

environmental variability that could destabi-

lize the chironomid community. Within the

province we sampled from four watersheds

(Fig. 1, Table 1): Puyango (3 394 km

, 0-3 285

m), Santa Rosa (2 805 km

, 0-2 900 m), Jubon-

es (2 153 km

, 0-3 900 m) and Siete (1 411 km

0-3 120 m) (Villamarín & Villamarín-Cortez,

2018). Forty rivers were sampled total dur-

ing the dry season between 2015 and 2016

(Fig. 1). The elevation gradient of sample sites

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ranged between 10 to 2 427 m and varied in

their degree of disturbance (ie. not impacted to

highly impacted). For the analyses we defined

three elevation bands: low (16 to 300 m; N = 17

rivers), mid (301 to 1 000 m; N = 14) and high

(> 1 001 m; N = 9).

Sampling and measurement of envi-

ronmental variables: We collected abiotic

samples using a 0.11 m

Surber net with

280-micron mesh light standardized at 1 m

(Manson, Wallis, & Hope, 2001). Nine benthic

samples were collected at each site and stored

in 96 % alcohol. Samples were separated into

families at the National Institute of Biodiver-

sity (INABIO) and taxonomic identifications

were made at the Research Laboratory of the

Universidad de Las Américas (UDLA) follow-

ing the nomenclature published in chironomids

specialized guides (Ruiz-Moreno, Ospina-Tor-

res, Gómez-Sierra, & Riss, 2000; Ruíz-More-

no, Ospina-Torres, & Riss, 2000; Epler, 2001;

Prat, Rieradevall, Acosta, & Villamarín, 2011).

We prepared plate mounts following the meth-

odology proposed by Epler (2001) to designate

chironomids morpho species.

Measurements of the chemical and physi-

cal parameters, hereafter referred to as environ-

mental variables, were collected in situ at each

sample site using a HACH multi-metric probe

(Loveland, CO, USA). We measured tem-

perature, dissolved oxygen, conductivity, total

dissolved solids and pH. Due to significant cor-

relations among environmental variables, we

did not include measurements of total dissolved

solids and temperature analyses.

Principal Component Analysis of envi-

ronmental parameters for each elevational

band: To understand the environmental fac-

tors associated with variation in elevation

we applied Principal Component Analysis

(PCA) (Clarke & Gorley, 2006). PCA effec-

tively reduces the dimensionality of covarying

variables without loss of information thereby

improving the interpretation of the results

Fig. 1. Sampling sites location in Southwest Ecuador. Basin and biomes information of each site is included.

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TABLE 1

Description of each studied site (river name, code, coordinates, altitude, biome) at of El Oro province, Ecuador

Códe River Name Coordinates WGS84 (UTM) Altitude (masl) Biome

EOP001 Riachuelo S/N Buenaventura 1 631 698 / 9 598 507 1 124 Foothill forest

EOP002 Río El Placer 634 599 / 9 596 436 1 311 Foothill forest

EOP003 Riachuelo S/N Buenaventura 2 638 334 / 9 600 616 1 095 Foothill forest

OP004 Río Buenaventura 638 934 / 9 598 359 1 003 Foothill forest

EOP008 Río Elvira 662 069 / 9 598 826 1 065 Foothill forest

EOP009 Río San Luis 669 052 / 9 592 458 1 472 Foothill forest

EOPO10 Río Pindo 651 584 / 9 583 798 562 Foothill forest

EOPO14 Río Amarillo 660 240 / 9 596 314 946 Foothill forest

EOP017 Riachuelo 3 Guizhaguiña 663 410 / 9 591 554 1 282 Foothill forest

EOP020 Riachuelo 3 Guizhaguiña 659 573 / 9 595 804 907 Foothill forest

EOP022 Río Naranjo 625 313 / 9 597 675 162 Dry lowlands forest

EOP023 Quebrada Los Sábalos 600 736 / 9 571 197 315 Dry lowlands forest

EOP024 Río Palmales 601 406 / 9 594 922 73 Dry lowlands forest

EOP025 Quebrada del Gallo 605 506 / 9 585 837 338 Dry lowlands forest

EOP027 Río Balsas 628 257 / 9 584 535 598 Foothill forest

EOP028 Río Marcabelí 619 227 / 9 580 988 499 Foothill forest

EOP029 Río Aguas Negras 615 636 / 9 582 190 561 Foothill forest

EOP030 Río Puyango 607 225 / 9 571 745 308 Dry lowlands forest

EOP032 Río S/N (sector la Cuca) 605 536 / 9 612 584 10 Dry lowlands forest

EOP033 Río Santa Rosa 616 778 / 9 613 980 33 Dry lowlands forest

EOP034 Río Arenillas 610 219 / 9 599 417 16 Dry lowlands forest

EOP035 Río Blanco 612 989 / 9 593 984 140 Dry lowlands forest

EOP036 Río Raspas 634 907 / 9 623 093 62 Dry lowlands forest

EOP037 Río San Agustín 633 089 / 9 623 505 50 Dry lowlands forest

EOP038 Río Palenque 639 395 / 9 626 001 90 Dry lowlands forest

EOP039 Río Siete 645 910 / 9 656 355 339 Foothill forest

EOP040 Río Pagua 637 895 / 9 658 807 20 Dry lowlands forest

EOP041 Río Bonito 638 800 / 9 656 191 38 Dry lowlands forest

EOP042 Río S/N (sector Cerro Azul) 641 597 / 9 611 712 1 131 Foothill forest

EOP043 Río Chilola 641 029 / 9 615 874 467 Foothill forest

EOP044 Río Dumari 637 322 / 9 616 378 267 Dry lowlands forest

EOP045 Río Buenavista 627 402 / 9 627 751 25 Dry lowlands forest

EOP046 Río Pivir 657 912 / 9 617 313 2 427 Montane forest

EOP049 Río Casacay 642 629 / 9 632 185 116 Dry lowlands forest

EOP050 Río Colorado 640 334 / 9 644 898 205 Dry lowlands forest

EOP051 Río San Jacinto 640 162 / 9 64 6942 126 Dry lowlands forest

EOP053 Río Changana 634 296 / 9 645 282 14 Dry lowlands forest

EOP054 Río Jubones 625 443 / 9 639 749 28 Dry lowlands forest

EOP055 Río Cune 653 296 / 9 632 175 349 Foothill forest

EOP057 Río Huizho 639 771 / 9 632 039 63 Dry lowlands forest

Vegetation in the low-elevation band consists of lowland dry forest and lowland deciduous forests (Sierra, 1999). Defining

characteristics of rivers in this band include stony substrates, silt, and sand with a strong flow rate. Evergreen forests

dominate the mid-elevation band (Sierra, 1999), and rivers have a lower proportion of sand than those rivers located in the

low-elevation band. At high elevation, evergreen forests dominate and rivers have a relatively slower flow rate. Upper basin

areas are comprised of well-preserved and minimally disturbed forest (Villamarín & Villamarín-Cortez, 2018) while mid and

lower elevations within the drainages have a high degree of agricultural exploitation and urban development.

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(Jollife & Cadima, 2016). The PCA was per-

formed in Primer6 (Clarke & Warwick, 1994).

Calculating Chironomid Diversity: Esti-

mates of diversity were calculated at the genus

level using Hill numbers (Chao et al., 2014;

Chao & Jost, 2015). Values for diversity (

can be interpreted as the effective number of

chironomid genera. Hill numbers of order q

represent richness (q= 0), exponential of Shan-

non’s entropy (q= 1) and the inverse Simpson

concentration (q= 2). Results are illustrated as

a continuous function of the parameter q (Chao

& Jost, 2015). The analysis was performed in

the iNext interactive web application (Hsieh,

Ma, & Chao, 2016).

Evaluating associations among Chiron-

omidae community and environmental fac-

tors: To determine the relationship between

chironomid community assembly and envi-

ronmental variables, we performed a Canon-

ical Correspondence Analysis (CCA) using

CANOCO software (Braak Ter & Barendregt,

1998). This technique determines the linear

combination of environmental variables and

community data that maximizes their correla-

tion (Borcard, Gillet, & Legendre, 2011) and

species order along the canonical axes indi-

cates their ecological optimum (Borcard et al.,

2011). Statistical significance was evaluated

using a Monte Carlo permutation procedure

(9999 permutations) (Braak Ter & Barendregt,

1998). Species ranking in the bottom 10 % of

abundances were removed prior to analysis to

prevent noise from rare taxa.

To understand genera-level contributions

to Bray-Curtis similarities among each eleva-

tional band, we performed a percentage of sim-

ilarity analysis (SIMPER; PRIMER6) (Clarke

& Warwick, 1994).

To understand the relationship among

distance, elevation and environmental vari-

ables on community composition, we applied

a Spearman rank correlation to the environ-

mental and biological dissimilarity matrices

and tested the statistical significance using

randomly permuted matrices (RELATE; 9999

permutations; Primer 6). Previously, the envi-

ronmental variables were normalized, while

the biological data were transformed using

log (x + 1), the distance and the elevation data

were not transformed. Three environmental

dissimilarity matrices were constructed using

environmental variables and site-level differ-

ences in geographic distance and elevation. The

community similarity matrix was comprised

of abundances of chironomid morphospecies.

Dissimilarities among environmental variables

were calculated using Euclidean distances

while Bray-Curtis similarity was applied to the

community matrix.

RESULTS

Environmental Variables: Environmental

variables exhibited substantial variation among

the three elevation bands (Table 2). Across all

elevational bands pH was consistently neutral

with little variation. Unusually high dissolved

oxygen content at low elevations was observed

in select sites such that mean values indicate

hyperoxic conditions. Conductivity was rela-

tively low at higher elevations and highest at

mid elevation, especially in sites exposed to

runoff from agriculture. Similarly, total dis-

solved solids were highest at lower elevations.

As expected, temperature was negatively cor-

related with the elevation.

The first principal component (PC1)

explained 37 % of the variance and dissolved

oxygen and conductivity weighed most heavily

(Fig. 2, Table 3). The second principal compo-

nent (PC2) explained 29.6 % of the variance

and pH and elevation weighed most heavily. In

general, higher loadings on PC1 and PC2 are

indicative of healthier aquatic environments.

Variation in samples from rivers in higher

elevations was attributed to variation in PC2,

whereas samples from middle elevations varied

more along PC1. Samples from low elevation

sites exhibited substantial variation across both

axes (Fig. 2).

Patterns in Chironomidae Abundance &

Diversity: For the three common subfamilies,

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densities at higher elevation were consistently

lower densities than densities at lower eleva-

tion (Fig. 3A). For the three elevation gradi-

ents, Chironominae was the most abundant

subfamily, with a marked increase at mid-ele-

vations. Tanypodinae was consistently the least

abundant subfamily across elevation gradients.

In contrast, Chironominae was the most abun-

dant in lower-elevation rivers.

There were 37 unique Chironomid genera

sampled and the greatest richness was observed

at high elevations (

D= 30) followed by low

elevation (

D = 30) and mid elevation (

D = 26)

TABLE 2

Mean values and standard deviations (SD) of environmental variables measured from studied sites

at el Oro province in Southwestern Ecuador

Environmental Variables

Low elevation N = 17 Middle elevation N = 14 High elevation N = 9

Mean SD Mean SD Mean SD

Elevation (m.a.s.l.) 62.7 48.1 475.8 225.7 1 323.3 438.8

PH 7.3 0.5 7.1 0.3 7.4 0.5

Dissolved Oxygen (mg/L) 13.8 6.7 11.4 2.7 12.2 1.8

Conductivity (µS/cm) 122.9 86.2 646.0 293.5 71.5 24.3

Temperature (°C) 25.1 2.0 23.0 2.3 19.6 2.3

Total Dissolved Solids (mg/L) 58.0 42.3 39.9 21.2 33.7 11.7

TABLE 3

Factor loadings and variance explained from Principal

Component Analysis (PCA) on environmental variables

from the studied sites at El Oro province,

in Southwestern Ecuador

PC 1 PC 2

% Variance of each component 37 29.6

% Accumulated Variance 37 66.5

Variables

Elevation 0.284

0.561

pH 0.388

-0.548

Dissolved Oxygen

0.656

-0.364

Conductivity

-0.581 -0.503

Fig. 2. PCA of the environmental variables and rivers from Southwestern Ecuador. The green dots correspond to the rivers

from higher elevations, the blue dots correspond to the rivers in the middle elevation, and the black dots to rivers from

lower elevations.

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(Fig. 4). Patterns of diversity were similar to

patterns of richness except for measures of

Simpson diversity for the low elevation (high:

= 9.55, q

= 4.99; mid: q

= 7.2, q

= 4.14;

low: q

= 7.86; q

= 3.92). However, differences

in diversity between the elevation categories

were not significant (F= 0.024, DF= 2, P >

0.05). The most dominant subfamilies included

Orthocladiinae (18 genera), Chironominae (11

genera), and Tanypodinae (8 genera). Pat-

terns of richness for the most representative

subfamilies varied by elevation (Fig. 3B).

Orthocladiinae was well represented across all

rivers, but the greatest richness was found in

rivers at higher elevation (> 1 000 m). Chirono-

minae richness was highest at mid-elevation,

followed by Orthocladiinae, and Tanypodinae.

The occurrence of Tanypodinae and Ortho-

cladiinae decreased with increasing elevation.

Fig. 3. A. Chironomids subfamilies densities of high,

middle, and low elevations from Southwestern Ecuador.

B. Chironomid subfamilies richness from Southwestern

Ecuador. The green bars correspond to high elevation

rivers; the blue ones correspond to mid-elevation rivers and

the black ones to low elevation rivers.

Fig. 4. Diversity observed using Hill numbers (q

= Richness, q

= Shannon diversity and q

= Simpsons Diversity) from

Southwestern Ecuador. Green dotted lines correspond to rivers of the high elevations; blue dots correspond to rivers of

middle elevations, and black dots correspond to rivers of low elevations.

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Tanypodinae was present in low densities at the

three elevation bands. Orthocladiinae richness

and density showed a clear trend to increase

with the elevation.

Relationships among Chironomidae

community and environmental variables:

In the Canonical Correspondence Analysis

(CCA), conductivity and dissolved oxygen

weighed heavily on the first axis, while pH and

elevation weighed on the second axis (Fig. 5A).

Rivers with high dissolved oxygen concentra-

tions, and low conductivity values are associ-

ated with the abundance of Parametriocnemus,

Cricotopus f4, Cricotopus sp3., Cricotopus

(Isocladius), Oliveiriella, Onconeura, Alotany-

pus, and Pentaneura (Fig. 5A). Rivers charac-

terized by high conductivity values, and low

oxygen dissolved concentrations are associated

with Cricotopus sp., Rheotanytarsus, Tanytar-

sus, Chironomus and Group Harnischia. While

several genera showed a preference for particu-

lar environmental conditions, others showed

no preference, primarily those generally dis-

tributed throughout the environmental gradient

such as Polypedilum, Oliveiriella, Cricotopus

f6, Hudsonimyia, Rheotanytarsus and Larsia

(Fig. 5A). The distribution of the sampling sites

in the ACC shows that the composition of the

chironomid community is influenced mainly

by the local characteristics of each site since

it does not show a significant separation in the

two-dimensional plane (Fig. 5B).

Spearman rank correlations (RELATE)

among Chironomid communities and water

quality parameters were not strongly nor sig-

nificantly correlated (P= 0.113; P= 0.0963).

Similarly, geographical distance (P= 0.049; P=

0.2267) and elevation (P= 0.042; P= 0.6976)

did not exhibit significant correlation to chiron-

omid community composition. The analyses

conducted in each elevation band do not show

correlation with the environmental characteris-

tics. Nevertheless, the Low Band (P = 0.098; P

= 0.217) had a better correlation, followed by

the High band (P= 0.056; P= 0.381) and the

Mid Band (P= -0.079; P= 0.742).

The SIMPER analysis revealed similar

distribution patterns to de CCA specially in the

dominant genera as is the case of Polypedilum,

Fig. 5. CCA of the environmental variables and genera of the Chironomidae family A. ▲: Othocladiinae genus; x:

Tanypodinae genus; +: Chironominae genus. B. ▲: correspond to the locations of the upper elevation range; ■: to those of

the middle elevation range and ●: of the lower elevation range).

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Chironomus, Group Harnischia, Cricitopus,

Tanytarsus (Table 4).

DISCUSSION

There is a strong influence of elevation

and conductivity on rivers from Southwestern

Ecuador. Elevation also tends to be associated,

directly and indirectly, with other environ-

mental components such as the productivity,

composition of the river bed substrate and veg-

etation, type of allochthonous material inputs

from adjacent ecosystem, and structure of

the river channel (Scheibler, Pozo, & Paggi,

2008; Acosta & Prat, 2010; Oviedo-Machado

& Reinoso-Flórez, 2018). While the variables

mentioned were not measured in our study, our

analyses reveal high environmental variation

that could influence both, biotic and abiotic

components, and define the composition and

structure of the chironomid community, espe-

cially variables that change along the gradient.

The positive relationship between tem-

perature and elevation is to be expected and

in turn affects processes of decomposition. In

lower elevations, microbial activity tends to be

higher (Acosta & Prat, 2010), which has impli-

cations on measured environmental variables

and the biological communities that inhabit the

rivers. Further, biomes in lower elevations are

predominantly dry (Briceño, Iniguez-Gallardo,

& Ravera, 2016; Escribano-Ávila, 2016) and

TABLE 4

SIMPER (Percentage of Similarity) analysis results for genus among studied sites grouped by elevation bands. In bold are

the values of the percentage of contribution of each genus to the similarity among sites of the same elevation band

Low elevation sites Middle elevation sties High elevation sites

Similarity 18.89 23.9 16.11

Genus

% Contrib. % Contrib. % Contrib.

Polypedilum

27.02 29.39

30.41

Tanytarsus

6.62

6.83

5.98

Pseudochironominii

4.2

9.75

4.29

Dicrotendipes

3.99

- -

G. Harnischia

3 1.28

3.06

Stenochironomus

1.83

0.83 0.95

Chironomus

- 0.16

0.61

Rheotanytarsus

9.44

8.5

Endotribelos

4.37

- -

Cricotopus sp.

17.65

8.38 6.15

Oliveriella

5.17

3.96 2.16

Parametriocnemus

3.66

- -

Stictocladius

2.57

- -

Género 1

1.01

- -

Cricotopus sp3.

0.69 0.47

5.45

Cricotopus (Isocladius)

2.86

0.2

Cricotopus f4

- -

1.76

Cricotopus f6

0.62

Onconeura

- -

0.84

Larsia

12.74

- 12.2

G. Thienemannimyia

2.7

12.03

6.24

Alotanypus

2.27

11.28

6.79

Pentaneura

0.5 0.77

3.69

Hudsonimyia

1.96

0.73

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inputs of allochthonous material differ from

those of the highlands, where the riparian forest

vegetation contributes to high and continuous

inputs of organic matter.

It is well known that temperature is a

strong driver for the distribution of macroin-

vertebrates along latitudinal and elevational

gradients (Dos Santos et al., 2018; Prat et al.,

2018). The distribution of chironomids has

been associated with temperature gradients

elsewhere (Acosta & Prat, 2010) including

Oliveiriella, Paraheptagya, Limaya and Paro-

chlus (Prat et al., 2011; Prat et al., 2018). In

our case, Chironominae was the most frequent

and dominant subfamily rivers at lower eleva-

tions while Orthocladiinae was more prevalent

in rivers at higher elevations. Temperature is

also strongly associated with oxygen solubility

(Jacobsen, 2003; Verberk, Bilton, Calosi, &

Spicer, 2011) such that the high-temperature

recorded in low elevation bands explain dis-

solved oxygen results in rivers sampled at

lower elevations. The considerable decrease in

oxygen at low elevation sites could be attribut-

able to the quantity of fine sediments with a

high organic load (López & Talero, 2015; Prat

et al., 2018; Sierpe & Sunico, 2019) and while

unusually high levels of dissolved oxygen at

other sites may be the result of eutrophication

(Harper & Phillips, 1992; Benjumea & Wills,

2007; Minaudo, Meybeck, Moatar, Gassama,

& Curie, 2015).

High and low elevation areas have similar

Chironomidae richness. Diversity was greatest

at high elevations due to the higher abundance

of more common species which is likely attrib-

utable to the greater water quality. At lower

elevations, the diversity of rare or unique spe-

cies is virtually zero compared to the other

elevations. In these lower sites we found spe-

cies capable of withstanding high tempera-

tures or reduced oxygen which indicates either

adaptations or phenotypic plasticity. Also, at

lower elevations, less geographical barriers

are found, which can contribute to a wider

distribution of the species. Rivers at low eleva-

tions are impacted by inputs from agricultural,

urban and mining practices especially gold

extraction (Villamarín & Villamarín-Cortez,

2018). We observed reduced diversity at mid-

elevation with much more stable communities

and unique genera relative to low-lying areas.

Studies in Ecuador are limited on this

taxonomic group and still under study (Roback

& Coffman, 1983; Prat, Acosta, Villamarín,

& Rieradevall, 2018; Hamerlik, da Silva, &

Jacobsen, 2019), a recent research by Hamer-

lik et al. (2019), identified 16 genera in the

upper Andean area of the Antisana Volcano

compared to the 30 genera found in our study.

Consequently, lowlands of the Andes can hold

a higher diversity of chironomids.

At subfamily level, we observed changes

in richness, abundance and diversity along

the elevation gradient, being Chironominae

the most dominant subfamily at lower eleva-

tions, characterized by lower dissolved oxygen

content and dominance of fine sediments with

high organic content (Acosta & Prat, 2010;

López & Talero, 2015).

While distribution patterns of subfamilies

have already been described, few studies take

place at genus level. We show that taxonomic

resolution reveals distinctive patterns of chi-

ronomid distribution along elevation gradients.

Our results suggest a clear turnover pattern

of dominant groups along the elevation gra-

dient considering the subfamily taxonomic

level as a boundary. However, several gen-

era showed specific preferences for particular

environmental conditions.

Orthocladiinae was more diverse at high

elevations. This might be due to the rocky

substrate, periphyton developed in rocks, low

or medium flow rates with steeper slopes,

which increases oxygen availability in rivers

at higher elevations. Hence, the trend of sub-

family composition relates to elevation, tem-

perature, dissolved oxygen, and total dissolved

solids. Therefore, different larvae morphotypes

of Cricotopus, Parametriocnemus, Oliveiri-

ella and Stictocladius, were mainly found on

high-elevation sites, which are characterized

by rivers with lower temperatures and stable

flow channels (Acosta & Prat, 2010; Hamerlik

et al., 2019); with rock and pebble substrates

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Rev. Biol. Trop. (Int. J. Trop. Biol.) • Vol. 69(1): 113-126, March 2021

(Oviedo-Machado & Reinoso-Flórez, 2018)

and fed mainly on algae and fine particulate

matter (Caleño, Rivera-Rondon, & Ovalle,

2018; Oviedo-Machado & Reinoso-Flórez,

2018).

The subfamily Chironominae tends to

increase its richness and abundance at lower

elevation areas (Acosta & Prat, 2010). As a

consequence, some genera have developed

adaptations, such as hemoglobin generation,

to optimize the use of limited amount of

oxygen available in these rivers (Oviedo-

Machado & Reinoso-Flórez, 2018). As the

elevation decreases, environmental characteris-

tics changed in our study sites. In lower eleva-

tion areas, temperature, flow, conductivity,

and dissolved solids increase. The increase in

water temperature reduces the availability of

dissolved oxygen, resulting in an increase in

chironomid genera with adaptations to these

conditions. The genera Chironomus, Steno-

chironomus, Tanytarsus, Rheotanytarsus, and

Polypedilum were dominant in lower-elevation

rivers. Several of them are considered tolerant

to low dissolved oxygen in water (López &

Talero, 2015) and generally inhabit pool areas

where fine sediment accumulates (Caleño et

al., 2018). A clear example of this is the prox-

imity found by in the CCA of the genera Tany-

tarsus and Rheotanytarsus to localities with

high concentrations of conductivity, which

correlated with the total dissolved solids, that

tend to accumulate in river pools as they use

this type of substrate to build houses (Caleño et

al., 2018; Oviedo-Machado & Reinoso-Flórez,

2018; Prat & García-Roger, 2018).

On other hand, there are changes in the

composition and abundance community whiles

the elevation increase. That is the case of

Tanypodinae that depends on the availability

of prey as they are predators of other macro-

invertebrates or other chironomids (Caleño

et al., 2018). Genera such as Alotanypus and

Thienemannimyia (Subfamily Tanypodinae)

were more abundant in areas with high dis-

solved solids while Hudsonimyia, Larsia, and

Pentaneura seem to have preferences for sites

with less dissolved solids at higher-elevation.

Tanypodins are known to be carnivorous chi-

ronomids with a preference for macroinver-

tebrates and animals (Caleño et al., 2018).

Therefore, their distribution relates to both

environmental characteristics and food avail-

ability. While tanypodins are predators, there

are some species that consume two types of

food (they feed on detritus and diatoms) when

prey is scarce (Da Silva & Ekrem, 2016).

In conclusion, the composition of the chi-

ronomid community showed changes in rela-

tion to the local environmental characteristics

measured, acting as a diversity driver of the

composition of Chironomidae. Chironomids

have a high dependence on local environmental

factors such as dissolved oxygen, pH, conduc-

tivity, and elevation. Nevertheless, the eleva-

tion and temperature were the most important

factors determining the chironomid community

composition. Moreover, the elevation acted as

a biogeographical barrier, with certain genera

restricted to high areas and others in low-lying

areas. Additionally, higher elevations are more

diverse due to a combination of environmental

characteristics and better-preserved drainages.

Ethical statement: authors declare that

they all agree with this publication and made

significant contributions; that there is no con-

flict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are

fully and clearly stated in the acknowledge-

ments section. A signed document has been

filed in the journal archives.

ACKNOWLEDGMENTS

This study was conducted within the

framework of the project “Development of

Guides of Mammals, Fish, Aquatic Macroin-

vertebrates and Flora with emphasis on Orchids

and Bromeliads of el Oro Province” pro-

posed by the GAD of el Oro and the INA-

BIO and the project AMB.CVF.17.03 from the

University of the Americas, Ecuador. Special

thanks to the Ministry of Environment of

Ecuador for providing the necessary permits

124

Rev. Biol. Trop. (Int. J. Trop. Biol.) • Vol. 69(1): 113-126, March 2021

(No. 004-IC-FLO-FAU-DPAEO-ME) for the

development of this project. To Nacís Prat for

the taxonomic review of the samples. To Mateo

Vega for the support in the generation of maps,

Daniel Padilla-Jiménez, Juan Manuel Guerra,

Nicole Cerón, Angie Ramírez, Daniel Donoso,

Carlo Escobar, Trujillo Sofía, Stephanie Flores,

Freddy Narváez, Alisson Pérez, and Andrea

Vaca for their support in the work of labo-

ratory and field.

RESUMEN

Controladores de diversidad y distribución altitu-

dinal de quironómidos (Diptera: Chironomidae) en los

Andes ecuatorianos. Introducción: Los quironómidos

(Diptera: Chironomidae) son los insectos acuáticos de

mayor diversidad y distribución mundial. A pesar de su

prevalencia en los sistemas lóticos, se sabe poco acerca de

su ecología y diversidad, especialmente de especies tropi-

cales en relación con otros taxones de insectos acuáticos,

particularmente en etapas inmaduras. Objetivo: Caracteri-

zar la diversidad de quironómidos a través de un gradiente

altitudinal en el suroeste de Ecuador, además de identificar

los parámetros fisicoquímicos asociados con su compo-

sición. Métodos: Las muestras se recolectaron utilizando

una red Surber en cuarenta ríos dentro de cuatro cuencas

hidrográficas en los Andes Sur del Ecuador, en ecosistemas

de bosques montanos y secos de tierras bajas abarcando

un gradiente altitudinal de 3 120 m.s.n.m. Se midie-

ron las variables fisicoquímicas: oxígeno, conductividad,

sólidos disueltos totales, temperatura y pH. Resultados:

En general, las variables ambientales se correlacionaron

fuertemente con la composición de las comunidades de

quironómidos. La variación en la comunidad de quironómi-

dos se asoció fuertemente con el oxígeno, la conductividad

y el pH. La presencia de los géneros Parametriocnemus,

Cricotopus f4, Cricotopus sp3, Cricotopus (Isocladius),

Oliveiriella, Onconeura, Alotanypus y Pentaneura se aso-

ció a temperaturas bajas, alto oxígeno disuelto y baja con-

ductividad, mientras que Cricotopus sp., Rheotanytarsus,

Tanytarsus y Chironomus se asociaron con alta conductivi-

dad y bajas concentraciones de oxígeno disuelto. El análisis

RELATE mostró que las características ambientales locales

determinan la composición de la comunidad de quironómi-

dos. Conclusiones: La similitud entre los factores ambien-

tales locales se correlacionó fuertemente con la similitud

entre los conjuntos de Chironomidae, especialmente con

variables como la concentración de oxígeno, el pH y la

conductividad, cuyas variables están altamente correlacio-

nadas con el uso de la tierra y la vegetación dominante en

las cuencas hidrográficas muestreadas.

Palabras clave: Andes tropicales; variables ambientales;

patrones de diversidad.

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