Claudia Patricia Ornelas-García

Evolutionary history of the fish genus Astyanax Baird & Girard (1854) (Actinopterygii, Characidae) in Mesoamerica reveals multiple morphological homoplasies.

BackgroundMesoamerica is one of the worlds most complex biogeographical regions, mostly due to its complex geological history. This complexity has led to interesting biogeographical processes that have resulted in the current diversity and distribution of fauna in the region. The fish genus Astyanax represents a useful model to assess biogeographical hypotheses due to it being one of the most diverse and widely distributed freshwater fish species in the New World. We used mitochondrial and nuclear DNA to evaluate phylogenetic relationships within the genus in Mesoamerica, and to develop historical biogeographical hypotheses to explain its current distribution.ResultsAnalysis of the entire mitochondrial cytochrome b (Cytb) gene in 208 individuals from 147 localities and of a subset of individuals for three mitochondrial genes (Cytb, 16 S, and COI) and a single nuclear gene (RAG1) yielded similar topologies, recovering six major groups with significant phylogeographic structure. Populations from North America and Upper Central America formed a monophyletic group, while Middle Central America showed evidence of rapid radiation with incompletely resolved relationships. Lower Central America lineages showed a fragmented structure, with geographically restricted taxa showing high levels of molecular divergence. All Bramocharax samples grouped with their sympatric Astyanax lineages (in some cases even with allopatric Astyanax populations), with less than 1% divergence between them. These results suggest a homoplasic nature to the trophic specializations associated with Bramocharax ecomorphs, which seem to have arisen independently in different Astyanax lineages. We observed higher taxonomic diversity compared to previous phylogenetic studies of the Astyanax genus. Colonization of Mesoamerica by Astyanax before the final closure of the Isthmus of Panama (3.3 Mya) explains the deep level of divergence detected in Lower Central America. The colonization of Upper Mesoamerica apparently occurred by two independent routes, with lineage turnover over a large part of the region.ConclusionOur results support multiple, independent origins of morphological traits in Astyanax, whereby the morphotype associated with Bramocharax represents a recurrent trophic adaptation. Molecular clock estimates indicate that Astyanax was present in Mesoamerica during the Miocene (~8 Mya), which implies the existence of an incipient land-bridge connecting South America and Central America before the final closure of the Isthmus of Panama (~3.3 Mya).

Untangling the evolutionary history of a highly polymorphic species: introgressive hybridization and high genetic structure in the desert cichlid fish Herichtys minckleyi

Understanding the origin of biodiversity requires knowledge on the evolutionary processes that drive divergence and speciation, as well as on the processes constraining it. Intraspecific polymorphisms can provide insight into the mechanisms that generate and maintain phenotypic, behavioural and life history diversification, and can help us understand not only the processes that lead to speciation but also the processes that prevent local fixation of morphs. The ‘desert cichlid’ Herichtys minckleyi is a highly polymorphic species endemic to a biodiversity hotspot in northern Mexico, the Cuatro Ciénegas valley. This species is polymorphic in body shape and trophic apparatus, and eco‐morphotypes coexist in small spring‐fed lagoons across the valley. We investigated the genetic structure of these polymorphisms and their phylogeographic history by analysing the entire control region of the mitochondrial DNA and 10 nuclear microsatellite markers in several populations from different sites and morphs. We found two very divergent mitochondrial lineages that most likely predate the closing of the valley and are not associated with morphotypes or sites. One of these lineages is also found in the sister species Herichthys cyanoguttatus. Data from neutral microsatellite markers suggest that most lagoons or drainages constitute their own genetic cluster with sympatric eco‐morphotypes forming panmictic populations. Alternative mechanisms such as phenotypic plasticity and a few loci controlled traits provide possible explanations for the sympatric coexistence of discrete nonoverlapping eco‐morphotypes with apparent lack of barriers to gene flow within multiple lagoons and drainages.

Morphometric variation between two morphotypes within the Astyanax Baird and Girard, 1854 (Actinopterygii: Characidae) genus, from a Mexican tropical lake.

Phenotypic variation is important for evolutionary processes because it can allow local adaptation, promote genetic segregation, and ultimately give rise to speciation. Lacustrine systems provide a unique opportunity to study the mechanisms by which sister species can co‐occur by means of ecological segregation. The fish genus Astyanax is characterized by high levels of phenotypic variability, providing an excellent model for the study of local specialization. Here, we analyze the morphological specializations through geometric morphometrics of two sympatric species described as different genera: Bramocharax caballeroi endemic to Lake Catemaco, and the widely distributed Astyanax aeneus. Additionally, we assess the correlation between phenotypic and genetic structure, and the phylogenetic signal of morphological variation. We examined body size and shape variation in 196 individuals and analyzed mitochondrial cytochrome b sequences in 298 individuals. Our results confirm the striking morphological divergence among the sympatric characids. Differences between them were mainly found in the body depth and profile and orientation of the head, where B. caballeroi in contrast with the A. aeneus, presented a fusiform body and an upward mouth. Moreover, different growth trajectories were observed among morphotypes, suggesting that a heterochronic process could be involved in the diversification of our study system. Morphological differences did not correspond with the molecular differentiation, suggesting high levels of homoplasy among the lineages of B. caballeroi morphs. J. Morphol. 275:721–731, 2014.

Phylogenetic relationships and evolutionary history of the Mesoamerican endemic freshwater fish family Profundulidae (Cyprinodontiformes: Actinopterygii).

Freshwater fishes of Profundulidae, which until now was composed of two subgenera, represent one of the few extant fish families endemic to Mesoamerica. In this study we investigated the phylogenetic relationships and evolutionary history of the eight recognized extant species (from 37 populations) of Profundulidae using three mitochondrial and one nuclear gene markers (∼2.9 Kbp). We applied a Bayesian species delimitation method as a first approach to resolving speciation patterns within Profundulidae considering two different scenarios, eight-species and twelve-species models, obtained in a previous phylogenetic analysis. Based on our results, each of the two subgenera was resolved as monophyletic, with a remarkable molecular divergence of 24.5% for mtDNA and 7.8% for nDNA uncorrected p distances, and thus we propose that they correspond to separate genera. Moreover, we propose a conservative taxonomic hypothesis with five species within Profundulus and three within Tlaloc, although both eight-species and twelve-species models were highly supported by the bayesian species delimitation analysis, providing additional evidence of higher taxonomic diversity than currently recognized in this family. According to our divergence time estimates, the family originated during the Upper Oligocene 26 Mya, and Profundulus and Tlaloc diverged in the Upper Oligocene or Lower Miocene about 20 Mya.

Phylogeographic analysis of genus Herichthys (Perciformes: Cichlidae), with descriptions of Nosferatu new genus and H. tepehua n. sp.

The genus Herichthys is widely considered to be the monophyletic representative of Cichlidae in northeastern Mexico and southern Texas. It is also the northernmost distributed genus of Neotropical Cichlids. Its distribution stretches over an area that is characterized by an intricate geologic and climatic history that affected its temporal and spatial diversification north of the Trans-Mexican Volcanic-Belt. We access the evolutionary history of the genus Herichthys based on a phylogenetic reconstruction using a mitochondrial fragment of gene Cox1. We evaluate its morphological variation, its correspondence with molecular differentiation and suggest a biogeographical scenario based on a molecular clock and demographic history. Furthermore, we describe Nosferatu new genus, composed of Nosferatu pame (assigned as type species), N. molango, N. pratinus, N. bartoni, N. labridens, N. pantostictus, and N. steindachneri. Genus is characterized by a transition to prolongation in the size of the symphysial pair of teeth relative to that of the other teeth in the outer row of the upper jaw; breeding pigmentation that consists of darkening of ventral area extending over nostrils, opercular series, or pectoral fins; depressed dorsal fin rarely expands beyond anterior third of caudal fin; and an elongated, elastic, smooth caecum adhered to a saccular stomach. We also describe Herichthys tepehua n. sp. found in the Pantepec, Cazones, Tenixtepec, Tecolutla, and Solteros rivers, in Veracruz, Mexico. Moreover, we provide re-descriptions for some of the species in Herichthys and propose a biogeographic hypothesis for both genera, based on available information on the geological and climate history of the area of study, associated to dating retrieved in our phylogenetic analysis.

Phylogenetic position of Magnivitellinum Kloss, 1966 and Perezitrema Baruš & Moravec, 1967 (Trematoda: Plagiorchioidea: Macroderoididae) inferred from partial 28S rDNA sequences, with the establishment of Alloglossidiidae n. fam.

Abstract The systematic position of two genera of Macroderoididae McMullen, 1937, Perezitrema Baruš & Moravec, 1967 and Magnivitellinum Kloss, 1966 is reviewed based on a phylogenetic analysis of the interrelationships of 15 species of the family allocated into six genera, along with 44 species of plagiorchioid trematodes, using partial sequences of the 28S rRNA gene. Sequences were analysed through parsimony, maximum likelihood and Bayesian inference. The obtained topologies show Perezitrema as the sister taxon of three species of Macroderoides Pearse, 1924; the latter genus appears to be paraphyletic since another three species are not included in this group. Instead, Magnivitellinum was placed as the sister taxon of Alloglossidium Simer, 1929. These relationships are well supported by high bootstrap and posterior probability values. The resulting trees demonstrate that the family Macroderoididae, as currently conceived in taxonomic treatments, is not monophyletic. Magnivitellinumsimplex Kloss, 1966 and Alloglossidium spp. were nested as sister taxa of members of the family Leptophallidae Dayal, 1938, whereas Perezitrema bychowskii Baruš & Moravec, 1967 and species of Macroderoides and Paramacroderoides Venard, 1941 were grouped with Auridistomumchelydrae (Stafford, 1900), a monotypic member of Auridistomidae Stunkard, 1924. Based on our results, a new family, Alloglossidiidae n. fam. was established to accommodate the genera Magnivitellinum and Alloglossidium.

The role of gene flow in rapid and repeated evolution of cave-related traits in Mexican tetra, Astyanax mexicanus

Understanding the molecular basis of repeatedly evolved phenotypes can yield key insights into the evolutionary process. Quantifying gene flow between populations is especially important in interpreting mechanisms of repeated phenotypic evolution, and genomic analyses have revealed that admixture occurs more frequently between diverging lineages than previously thought. In this study, we resequenced 47 whole genomes of the Mexican tetra from three cave populations, two surface populations and outgroup samples. We confirmed that cave populations are polyphyletic and two Astyanax mexicanus lineages are present in our data set. The two lineages likely diverged much more recently than previous mitochondrial estimates of 5–7 mya. Divergence of cave populations from their phylogenetically closest surface population likely occurred between ~161 and 191 k generations ago. The favoured demographic model for most population pairs accounts for divergence with secondary contact and heterogeneous gene flow across the genome, and we rigorously identified gene flow among all lineages sampled. Therefore, the evolution of cave‐related traits occurred more rapidly than previously thought, and trogolomorphic traits are maintained despite gene flow with surface populations. The recency of these estimated divergence events suggests that selection may drive the evolution of cave‐derived traits, as opposed to disuse and drift. Finally, we show that a key trogolomorphic phenotype QTL is enriched for genomic regions with low divergence between caves, suggesting that regions important for cave phenotypes may be transferred between caves via gene flow. Our study shows that gene flow must be considered in studies of independent, repeated trait evolution.

Trophic specialization and morphological divergence between two sympatric species in Lake Catemaco, Mexico

Abstract The association of morphological divergence with ecological segregation among closely related species could be considered as a signal of divergent selection in ecological speciation processes. Environmental signals such as diet can trigger phenotypic evolution, making polymorphic species valuable systems for studying the evolution of trophic‐related traits. The main goal of this study was to analyze the association between morphological differences in trophic‐related traits and ecological divergence in two sympatric species, Astyanax aeneus and A. caballeroi, inhabiting Lake Catemaco, Mexico. The trophic differences of a total of 70 individuals (35 A. aeneus and 35 A. caballeroi) were examined using stable isotopes and gut content analysis; a subset of the sample was used to characterize six trophic and six ecomorphological variables. In our results, we recovered significant differences between both species in the values of stable isotopes, with higher values of δ15N for A. caballeroi than for A. aeneus. Gut content results were consistent with the stable isotope data, with a higher proportion of invertebrates in A. caballeroi (a consumption of invertebrates ten times higher than that of A. aeneus, which in turn consumed three times more vegetal material than A. caballeroi). Finally, we found significant relationship between ecomorphology and stable isotopes (r = .24, p < .01), hence, head length, preorbital length, eye diameter, and δ15N were all positively correlated; these characteristics correspond to A. caballeroi. While longer gut and gill rakers, deeper bodies, and vegetal material consumption were positively correlated and corresponded to A. aeneus. Our results are consistent with the hypothesis that morphological divergence in trophic‐related traits could be associated with niche partitioning, allowing the coexistence of closely related species and reducing interspecific competition.

Functional modularity in lake-dwelling characin fishes of Mexico

Modular evolution promotes evolutionary change, allowing independent variation across morphological units. Recent studies have shown that under contrasting ecological pressures, patterns of modularity could be related to divergent evolution. The main goal of the present study was to evaluate the presence of modular evolution in two sister lacustrine species, Astyanax aeneus and A. caballeroi, which are differentiated by their trophic habits. Two different datasets were analyzed: (1) skull X-rays from 73 specimens (35 A. aeneus and 38 A. caballeroi) to characterize skull variation patterns, considering both species and sex effects. For this dataset, three different modularity hypotheses were tested, previously supported in other lacustrine divergent species; (2) a complete body shape dataset was also tested for four modularity hypotheses, which included a total of 196 individuals (110 Astyanax aeneus and 86 A. caballeroi). Skull shape showed significant differences among species and sex (P < 0.001), where Astyanax caballeroi species showed an upwardly projected mandible and larger preorbital region. For the skull dataset, the modularity hypothesis ranked first included three partitioning modules. While for the complete body dataset the best ranked hypothesis included two modules (head vs the rest of the body), being significant only for A. caballeroi.

Edmundo Díaz Pardo (1945–2013)

E MINENT Mexican ichthyologist EDMUNDO DÍAZPARDO passed away 6 November 2013 in the City of La Piedad, State of Michoacán, Mexico, at the age of 68. ‘‘Mundo,’’ as he was known to his students, friends, and colleagues, was a dedicated educator, academic, and mentor who enthusiastically shared his experience and knowledge of Mexican ichthyology with numerous generations of students at various institutions in Mexico, Europe, and North and Central America. Edmundo was born in Mexico City on 20 November 1945 to Gregorio Dı́az Palacios and Clemencia Pardo Alegre. He majored inBiology in 1969at theEscuela NacionaldeCienciasBiológicas of the Instituto Politécnico Nacional (ENCB-IPN) in Mexico City. His undergraduate thesis ‘‘Anatomı́a del tubo digestivo de Lepisosteus tropicus Gill, 1863’’ (Anatomy of the digestive tract of Lepisosteus tropicus Gill, 1863) was one of the first of his many contributions to ichthyology and natural resources conservation in Mexico. After graduation, he continued his education at ENCB-IPN, where he completed M.S. and Ph.D. degrees in 1980 and 1992, respectively. While completing his graduate degrees, he also served several roles at ENCB-IPN. He was Chief and Curator of the Laboratory of Chordates between 1975–1991, and later Chief and Curator of the Ichthyology and Limnology Laboratorybetween1991–2001.After retiring from the Instituto Politécnico Nacional in 2002, he went on to become a professor at the Facultad de Ciencias Naturales (Biology) of the Universidad Autónoma de Querétaro (UAQ), where he founded and served as Curator of the Central Mexico Fish Collection. Edmundo’s academic activity transcended education and research institutions. He co-founded the Mexican Ichthyological Society (SIMAC), which he later led as President between 1998 and 2000. In recognition of his work in the society and as an academic, SIMAC appointed him in 2006 as an Honorary Member. He also co-founded the Mexican Association of Limnology and the Mesoamerican Network of Biotic Resources, a group dedicated to conservation and biological research throughout Mesoamerica. Sharing his knowledge about natural resources and ichthyology was important to Edmundo; throughout his career he gave more than 100 conference presentations and invited talks at diverse venues, both in Mexico and abroad. In addition to his work with scientific societies, Edmundo was a soughtafter authority who participated in the design of several regulations and codes for the legal protection of natural resources in Mexico. He participated as a member of the commissions responsible for designing the official Mexican 1994, 2001, and 2010 ‘‘red lists’’ (generally identified as NOM-ECOL-059) identifying species at risk or under a special conservation status. Despite being a recognized academic and having served many important administrative roles at research institutions, Edmundo was adamantly against elitism in the academic realm; it was easy to get him going against superiority in academia. Edmundo understood the value of zoological collections and fomented their formation and use. Following the steps of his mentor, Dr. José Álvarez del Villar, he expanded and established several fish collections at numerous academic institutions in Mexico. In addition to the expansion of the Ichthyological Collection at ENCB (with acronym COPEMEX, ENCB-IPN-P), he also worked on establishing the fish collections at the Universidad Autónoma de Querétaro (UAQ–PCM) and the Universidad Autónoma de Morelos (CP-UAEM); these two collections today bear his name. He, along with other important already departed ichthyologists including J. Álvarez del Villar, Salvador Contreras Balderas, and Andrés Reséndez Medina, can be considered among the pillars of ichthyology in Mexico. Edmundo’s international academic activity included work as a visiting researcher with Dr. C. L. Hubbs (Scripps Institution of Oceanography, University of California–San Diego) in 1973. In 2000 he participated as a visiting researcher at the Museo Nacional de Ciencias Naturales de Madrid, Spain, where he actively collaborated with Dr. I. Doadrio Villarejo. In 2008 he was a guest academic at Auburn University (Alabama, USA). In the late 2000s he also interacted with numerous collaborators in Nicaragua, Guatemala, and Costa Rica via the Mesoamerican Network of Biotic Resources. Throughout his career he worked in close collaboration with several U.S.-based scientists with interests in Mexican fishes (e.g., Henry L. Bart–Tulane University; John Lyons–University of Wisconsin; Barry Chernoff–Wesleyan University, among many others), which often resulted in new discoveries and advances in our knowledge of freshwater fishes. Edmundo was a teacher for numerous generations of biologists at the Instituto Politécnico Nacional, the Universidad Autónoma del Estado de Morelos, the Universidad Autónoma de Querétaro, and the Universidad Michoacana