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Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71: e50081, enero-diciembre 2023 (Publicado 27 de enero, 2023)
such as those of the Western Chaco dry forest,
are still scarce. Nevertheless, recent studies that
analyzed benthic macroinvertebrates distribu-
tion in rivers of the Western Chaco ecoregion
revealed that chironomids are the most abun-
dant invertebrate group (Leiva et al., 2020; Pero
et al., 2019).
In addition, it is also important to know the
seasonal variations of freshwater ecosystems
features across contrasting climatic but contig-
uous regions, mainly because of the uncertain
challenges of climate change (Tonkin et al.,
2019) and for the inference of reference con-
ditions for the bioassessment (Hawkins et al.,
2010). Some studies associated seasonal dis-
turbances in streams, such as spates and floods,
as important features structuring Chironomidae
assemblages (Langton & Casas, 1998; Rossaro
et al., 2006). The relative abundance of Chi-
ronomidae subfamilies also showed temporal
variation in neotropical streams, such as those
of Yungas forest. For example, Orthocladiinae
was better represented during low water period
whereas Chironominae was more abundant in
high-water period (Tejerina & Malizia, 2012).
Nonetheless, Acosta and Prat (2010) found that
in both the dry and rainy seasons, the subfamily
Orthocladiinae was dominant, surpassing 70 %
of the total of Chironomidae in high elevation
streams of Andean region of Peru.
It is important to know the distributional
variations of these aquatic insects in reference
conditions along the landscape to improve
water quality bioassessments (Nicasio & Juen,
2015) and extend our knowledge about how
climatic and ecoregional gradients influence
the distribution and function of the freshwater
neotropical biota. Therefore, our main goal was
to explore the vertical and spatial distribution
of chironomids in Northwestern Argentina,
expanding the study area in the Yungas Forest
with respect to Tejerina and Malizia (2012) and
including a comparative analysis with rivers of
the little-explored and highly threatened West-
ern Chaco ecoregion (which represent the first
specific study on chironomids for this region).
Hence, we aimed to answer: (1) How do the
composition and structure of Chironomidae
assemblages (genus and subfamilies) vary
between Yungas and Western Chaco ecoregions
and among mountains, foothills and lowlands
in Northwestern Argentina? (2) How do com-
position and structure of Chironomidae vary
between hydrological seasons (low and high-
water periods)? (3) How is Chironomidae dis-
tribution related to the environmental features
of the studied rivers?
MATERIALS AND METHODS
Study Area: The study area is located
between (26°-28° S & 66°-64° W) and covers
approximately 20 000 km2 including most of
Tucumán province and its limits with San-
tiago del Estero province in Northwestern
Argentina (Fig. 1). In this study, we sampled
reaches of fluvial channels located in two dif-
ferent ecoregions: Yungas subtropical cloud
forest and Western Chaco dry forest (Brown &
Pacheco, 2006).
The Yungas subtropical cloud forest or
Yungas forest is a narrow belt of mountain
rainforest, ranging from 400 to over 3 000
m.a.s.l. (Brown, 2000). The climate is warm
and humid, with annual average temperatures
ranging from 14 to 26 °C and rainfall from
1 000 to 2 500 mm (Brown et al., 2001). The
Yungas forest is stratified into 3 vegetation
belts. In general, Yungas altitudinal levels are
not considered sub-ecoregion units, but in this
study, we evaluated them as differentiated units
within the Yungas forest because each altitudi-
nal level presents particular climatic features
and floristic composition (Brown & Pacheco,
2006). The high montane forest (1 500-3 000
m.a.s.l.) contains monospecific tree stands that
are usually either Alnus acuminata (Kunth) or
Podocarpus parlatorei (Pilg.). Annual rainfall
reaches 1 000 mm. The low montane for-
est (700-1 500 m.a.s.l.) has the most diverse
vegetation, with many evergreen species, and
is dominated by Cinnamomum porphyrium
(Griseb.) Kosterm. and Blepharocalyx salicifo-
lius (Kunth) O. Berg. The low montane forest
also has the highest precipitation (2 000 mm
annual) and least seasonal hydrological regime.