Panbiogeographical analysis of Costa Rican freshwater fishes

Track analysis and Parsimony analysis of endemicity (PAE) were performed to analyze the distribution pattern of Costa Rican freshwater fishes. A basic matrix (presence/absence) was prepared using the distribution of 77 freshwater fish. The data were analyzed with CLIQUE software in order to find generalized tracks (cliques). Data also were analyzed with the software NONA and Winclada version 1.00.08 in order to perform the Parsimony Analysis of Endemicity (PAE). Fourteen equally probable cliques were found with 31 species in each and the intersection of the amount was selected as a generalized track dividing the country in two main zones: Atlantic slope from Matina to Lake Nicaragua and Pacific slope from the Coto River to the basin of the Tempisque River connected with some branches oriented to the central part of the country. PAE analysis found ten cladogram areas (72 steps, CI=0.45, RI=0.64), using the “strict consensus option” two grouping zones were identified: Atlantic slope and Pacific slope. Both PAE and Track Analysis show the division of the two slopes and the orientation of the generalized track suggests new biogeographical evidence on the influence of both old and new southern elements to explain the migrations of freshwater fish into Central America during two different geological events. Rev. Biol. Trop. 56 (1): 165-170. Epub 2008 March 31.

Costa Rica, whose territory comprises 52 100 km 2 (0.03 % of the total surface of the planet), possesses about 5 % of the total diversity described thus far in the world.This diversity includes 135 freshwater fish species (19 endemic) of 350 reported for Mesoamerica, which extends from Tehuantepec isthmus in the south of Mexico as far as northern Colombia.Moreover three of the four ichthyic Mesoamerican provinces converge in Costa Rica: Chiapas-Nicaragua and Isthmian in the Pacific slope and San Juan in the Atlantic slope (Bussing 1976(Bussing , 1985(Bussing , 2002)).
Costa Rica's continental ichthyofauna possesses a geographical distribution influenced by both northern continent and principally the southern continent.Bussing (1985) and Briggs (1994) argue that the colonization of the Central American families Characidae, Pimelodidae, Poecilidae and Cichlidae, occurred during the Cretaceous/Paleocene, 60 million years ago, a period in which the existence of the old connection permitted the dispersion of the South American species.This connection disappeared during the Tertiary, Central America's separation from South America permitted the development of endemic lineages (Bussing 1976).
Finally a new connection appeared by the Pliocene (Pitman et al. 1993), allowing a new dispersion through Central America.
Few studies have been made on the distribution, systematics and biogeography of middle American Cichlids (Bussing 1985, Bussing 2002, Roe et al. 1997, Martin and Birmingham 1998).The capacity of track analysis to find relationships among ancestral biota given a panbiogeographical approach that emphasizes the spatial and geographical dimension of biodiversity is an important tool in order to begin the identification of evolutionary processes.Roe et al. (1997), and Martin and Birmingham (1998) contributed with molecular and ecological information, which is a good initiative in order to comprise the biogeography and evolutionary history of Mesoamerican freshwater fish.Given the necessity for knowledge in this area and on features in Costa Rica, we consider it useful to contribute new biogeographical evidence utilizing Track Analysis and Parsimony Analysis of Endemicity (PAE) evaluate the distribution of the Costa Rican freshwater fish.
In order to perform the Track Analysis (Craw 1989) a basic matrix of taxa/area was constructed (presence coded "1" and absence coded "0") (Table 2) and analyzed using the Clique-compatibility software (Felsenstein 1986).The total number of cliques (tracks) was determined and the longest was established as Fig. 1.Generalized track depicted over the Costa Rican basins, obtained from Panbiogeographical analysis.Atlantic slope: LN=Lake Nicaragua, RF=Frío River, SJ=San Juan River, SC=San Carlos River, SA=Sarapiquí River, TO=Tortuguero River, PA=Parismina River, MA=Matina River, SI=Sixaola River.Pacific slope: NI=Nicoya peninsula's Rivers, TM=Tempisque River, BE=Bebedero River, BA=Barranca River, TA=Tárcoles River, PI=Pirris River, TE=Térraba River, CO=Coto River.a generalized track and drawn by using a minimal spanning tree method.Parsimony Analysis of Endemicity was performed according to Morrone (1994), utilizing the basins previously established as geographical operators.A hypothetical ancestral area coded with zero to all characters was included to root the tree.The matrix was analyzed using the software NONA (Goloboff 1993) and Winclada version 1.00.08 (Nixon 1999).

RESULTS
A total of 14 equally probable cliques containing 31 species were obtained.The intersection of the amount resulting the species was selected as generalized track: Aequidens coeruleopunctatus, Amphilophus lyonsi, Archocentrus myrnae, A.  PAE put forward a total of ten area cladograms, strict consensus obtained with 72 steps, CI=0.45 and RI=0.64 (Fig. 2).Two main groups were identified one of them containing four species: Theraps sieboldii, Poeciliopsis turrubarensis, Arius seemanni and Dormitator latifrons, and including the basins BA, TA, CO, PI, TE, BE, TM, NI.The second group was defined by two species Theraps underwoodi and Brachyrhaphis holdridgei, including the basins SA, PA, SI, MA, TO, SJ, LN, and SC (Fig. 2).

DISCUSSION
Empirical observations of the current distribution of the Central American freshwater fish showed two main groups with distinct spatial and temporal origins (Bussing 1976(Bussing , 1985)).The old northern element presents a major quantity of species in the Atlantic slope and some representatives in the Pacific slope (e.g.Astyanax, Poecilia, Priapichthys, Neoheterandria, Amphilophus, Archocentrus, and Astatheros).In contrast, the new southern element has a major quantity of species in the Pacific slope (e.g.Pterobrycon, Nannorhamdia, Brycon, Roeboides, Pseudocheirodon) which is reflected in the track analysis with two main tracks, one in the Pacific and other in the Atlantic slope, separated at the south of the country by the Talamanca mountain range.
With PAE the separation of two slopes was also observed (Fig. 2), and seven of fifteen endemic species utilized were found in the Isthmian province.Therefore the influence of a new southern element after Pliocene with regard to genera composition and distribution (Bussing 1985) was corroborated in light of our analysis.In fact, the Terraba and Pirris basins form an endemic area within the Isthmian province due to the number of endemic species (Fig. 2).Lundberg (1993) reported fossil cichlids (located in the old genus Cichlasoma) found in the Antilleans and dated to the early Miocene when the Caribbean islands were possibly formed from Central America.Given the physiological characteristics of this family, tolerant to salinity (secondary type), it is presumed that cichlids were among the first inmigrants from the southern continent as revealed in the appearance of the old southern element.Later vicariant events and the reestablishment of the isthmus (Bussing 1985), originate different lineages of the new southern element.
In conclusion, both PAE and track analysis illustrate the separation of two slopes.The orientation of the generalized track suggests new biogeographical evidence about the influence of both old and new southern elements, and the aggregation pattern found with PAE  2. The black circles represent the apomorphic changes.Note the two main groups defined by four species in group one (Pacific slope) and two species in group two (Atlantic slope).
suggests inmigration associated with different geological periods.More detailed analyses are needed in order to solve cladistic biogeography problems related to Costa Rica and Central America's freshwater fishes.
Fig.1depicts two regions of spatial homology, one in the Atlantic slope from the southern part of the country to Lake Nicaragua and the other on the Pacific slope from the basin of Coto River to Tempisque River basin, which is connected with Frío River basin and some bifurcations toward the central region of the country.

Fig. 2 .
Fig. 2. Strict consensus cladogram obtained from PAE applied to the matrix in Table2.The black circles represent the apomorphic changes.Note the two main groups defined by four species in group one (Pacific slope) and two species in group two (Atlantic slope).

TABLE 1
Species list utilized in the analyses *Endemic species from Costa Rica.

TABLE 2
Matrix obtained including the distribution of 77 species of freshwater fishes of Costa Rica, see numbers in table 1 to see the species number