Irene de los A. Barriga-Sosa

Molecular phylogeography of Pteronotus davyi (Chiroptera: Mormoopidae) in Mexico

Abstract Pteronotus davyi, Davys naked-backed bat, is a tropical bat whose current distribution in Mexico covers the watersheds of the Pacific and the Gulf coasts of Mexico, converges at the Isthmus of Tehuantepec, and continues into the Yucatan peninsula. We evaluated phylogeographic relationships among 18 populations in Mexico using data from the nucleotide sequence of the hypervariable II domain of the mitochondrial DNA control region from 105 specimens. Extant populations were distributed over 3 geographic regions (Pacific Coast, Gulf Coast, and Southeastern) that were delineated a priori according to floristic characteristics and biogeography. Coalescent simulations supported a phylogeographic model of 2 refugia situated in the south of Mexico (Arc and Soconusco refuges) during the late Pleistocene, followed by expansion into Pacific Coast, Gulf Coast, and Southeastern groups. The populations of the Southeast were genetically divergent from the Pacific and Gulf Coast populations, supporting the existence of 2 distinct lineages of P. davyi in Mexico, likely due to the Isthmus of Tehuantepec acting as a geographical barrier. Examination of our data revealed genetic differentiation of the Pacific and Gulf coastal groups but at a lower level relative to the Southeast. This pattern suggests that the Sierra Madre Occidental, Sierra Madre Oriental, and Sierra Madre del Sur act as physical barriers to dispersal for P. davyi.

Taxonomic Status Assessment of the Mexican Populations of Funnel-Eared Bats, Genus Natalus (Chiroptera: Natalidae)

Due to its morphological conservatism, the American funnel-eared bats of the genus Natalus have had a complex taxonomic history. In Mexico only one species, N. stramineus, has traditionally been recognized. But recently a new endemic species, N. lanatus, was described in the region as a sympatric sibling species of N. stramineus. Natalus stramineus, with a geographic distribution extending from Mexico to Panama, was subsequently reassigned to N. mexicanus. In this study, we analyzed morphological and molecular characters to determine if two distinct species of funnel-eared bats (N. lanatus and N. mexicanus) occur in Mexico. We found that the proposed diagnostic morphological characters that separate the two taxa are not consistent and rarely differentiate between the two forms. Likewise, phylogenetic analyses do not support the separation of Natalus into two species in Mexico, but there is clearly geographic structure when all Mexican haplotypes are combined. The genetic distance between the haplotypes that could be ascribed to N. lanatus and N. mexicanus was typically within the range of conspecifics and not distinct species. To summarize, the results of both morphological and molecular analyses point to the presence of a single species of Natalus in Mexico.

Optimization of Triploidy Induction in the Pacific White Shrimp, Litopenaeus vannamei

Abstract We describe the results of the optimization process to induce triploidy in the Pacific white shrimp, Litopenaeus vannamei, reported the diploid and triploid chromosome numbers, the time of the extrusion of the second polar body and the survival rate at the nauplii larvae stage. The diploid chromosome number was 88 (42.5%). The extrusion of the second polar body was observed in eggs within 16 and 20 minutes post-spawning, the higher frequency occurred at 18 minutes. The triploid chromosome condition was induced by application of cold shock (10°C) to eggs 20 minutes after fertilization and with a duration of 15 minutes. We obtained a high eclosion rate (79%) in comparison to other studies. The verification of triploid nauplii larvae in mitotic metaphase showed a chromosome number set of 132.

Genetic introgression of cultured rainbow trout in the Mexican native trout complex

Abstract The Mexican native trout complex is the group of salmonids that naturally has the southernmost distribution in the world. Despite its unique status and evidence of more than 13 distinct lineages, there are only two described species (Oncorhynchus mykiss nelsoni and O. chrysogaster). These fishes are threatened by environmental and anthropogenic factors, most notably the introduction of the exotic species O. mykiss (rainbow trout) for aquaculture. Here we applied population genetics analysis in 1,017 wild and cultured trout to understand the extent of genetic introgression of rainbow trout in Mexican native trout. Present results indicate a high degree of introgression and genetic admixture among introduced rainbow trout and some populations of Mexican native trout, exposing them to loss of genetic diversity. Thus, introduction of exotic trout for aquaculture purposes must be strictly regulated or avoided and we advise the use of native trout for aquaculture.

Clarifying the taxonomic status of Merluccius spp. in the northeastern Pacific: a combined morphological and molecular approach

The taxonomic status of hake (Merluccius spp.) in the northeastern Pacific is unclear. Hakes in this region are Merluccius productus, M. angustimanus, M. hernandezi, and a morphotype known as dwarf hake. Of these, only the first two species are currently valid. Descriptions in previous studies have been limited by overlapping morphological characteristic, lack of biological material, and limited numbers of sampling localities. To clarify their taxonomy, 461 hake were obtained from eight localities along the North American coast for morphological and mitochondrial DNA sequence analyses (cytochrome b, cytochrome c oxidase subunit I, and 16S ribosomal rDNA). Morphological and molecular analyses suggest that hake in this region represent a continuum of a single species with some levels of morphological and genetic intra-specific variation. In light of these results, we propose that M. productus is the only species of hake present along the North American and northern Central American coast.

Low but Significant Subdivision among Populations of Chirostoma grandocule from Lake Patzcuaro, Mexico

ABSTRACT We examined morphological and genetic data for Chirostoma grandocule, the most abundant silverside fish from Lake Pátzcuaro, Michoacán, México, as part of a larger project to clarify the genetic structure of the genus. We analyzed 19 morphometric, 8 meristic, and 11 putative enzyme-coding loci from C. grandocule samples from two different localities within the lake during three different years (Janitzio 1996, 1999, and Ichupio 1997). Because morphometric attributes were all correlated, scores derived from reciprocal averaging analysis were used to describe the variation in fish morphology. Discriminant analysis using 10 morphometric and 8 meristic variables revealed significant differences between samples (Janitzio and Ichupio, χ2 = 558.4 and 531.5, P < 0.001, respectively). The utilization of morphometric features for the reclassification of organisms into the site of origin was highly effective (x̄ = 98.2%). Allozyme data resolved seven polymorphic loci (P0.99) and levels of heterocigosis that ranged from 0.0134 to 0.0319 (x̄ He = 0.0234). Weir and Cockerhams F-statistics provided evidence of low but significant heterogeneity between sites and years (jackknifed θS = 0.0252, SD = 0.0126); a pairwise comparison of θS values revealed that the sample from Ichupio was highly distinct compared to the samples from Janitzio (0.0400 vs. 0.0033, P < 0.05), indicating intra-lacustrine differentiation between the north and south samples. Genetic co-ancestry distances between samples ranged from 0.0154 to 0.0341. The genetic and morphometric variation detected in C. grandocules samples are discussed in the light of differences in sex ratio and of the contrasted environmental and physio-geographical intra-lacustrine conditions.

CLOSE GENETIC RELATIONSHIPS BETWEEN TWO AMERICAN OCTOPUSES: OCTOPUS HUBBSORUM BERRY, 1953, AND OCTOPUS MIMUS GOULD, 1852

ABSTRACT The octopuses Octopus hubbsorum and Octopus mimus are two species of octopuses that inhabit shallow waters of the eastern Pacific Ocean. The former species is found in the north, from the Gulf of California to Oaxaca, Mexico, whereas O. mimus lives in the south, from Peru to Chile. To infer the phylogenetic relationships between these species we used the mitochondrial genes cytochrome oxidase subunits I and III, and r16S with the aim of comparing their genetic distances with those of other Octopus sp. The genetic distance values between both species estimated per gene or concatenated were low (0%–1.6%) in comparison with other interspecific distances values (4.6%–18.4%). Application of 10× rule showed there is no overlap between intra- and interspecific octopus distances, whereas the application of the 4× rule confirmed that both octopuses belong to the same lineage. The resolved topologies with maximum parsimony and Bayesian approaches clustered the specimens of O. hubbsorum and O. mimus in a single clade with high bootstrap and posterior probability values (100 and 1.0, respectively). These results allow us to suggest that O. hubbsorum and O. mimus could represent the same species.

Genetic evidence of the presence of Octopus mimus in the artisanal fisheries of octopus in Santa Elena Peninsula, Ecuador

Abstract: The geographic distribution of Octopus mimus Gould, 1852 is unclear, as most records are restricted to coastal localities of Peru and Chile, and some references have mentioned its presence off Central America. It is unknown whether this octopus is found off Ecuador as two previous unpublished records have suggested. The aim of the present study is to identify genetically the main octopus captured in a marine protected area known as Reserva de Produccion Faunistica Marino-Costera Puntilla de Santa Elena (REMACOPSE) off the Santa Elena peninsula, Ecuador. Samples collected from the local fishery were used to test the presence of this species based on the sequences of three mitochondrial markers and using a Bayesian approach. The phylogenetic analysis confirms that O. mimus inhabits the REMACOPSE. The results also indicate that the octopus specimens captured in the fishery from this marine protected area, are more closely related to O. mimus specimens from Central America than those from South America. The genetic identification of two groups of O. mimus could be associated with the different marine environmental conditions of the two biogeographic provinces. The finding in this study represents an important step for posterior research on the biology and fishery of octopus in Ecuador.

Conservation units of Pteronotus davyi (Chiroptera: Mormoopidae) in Mexico based on phylogeographical analysis

The analysis of genetic diversity is routinely used to identify divergent intraspecific units and contribute to the knowledge base of biodiversity. In this study we used mitochondrial genetic diversity to propose three management units (MUs) for the Davys nakedbacked bat (Pteronotus davyi), an insectivorous forest-dwelling species that is distributed in tropical and subtropical areas of America. We analyzed a 555 bp segment of the mitochondrial DNA (mtDNA) control region in 144 individuals from 18 localities spread across the species distribution range in Mexico. Our results demonstrated that the mitochondrial genetic diversity of P. davyi is distributed in three MUs, namely Gulf North, Pacific-Veracruz and Southeastern, with conservation priority, due to either the high mitochondrial genetic diversity or the high proportion of unique haplotypes, for the following populations: Playa de Oro, Arroyo del Bellaco and Catemaco in the Pacific-Veracruz region, and Agua Blanca, Sardina, Calakmul, Calcehtok and Kantemó from the Southeastern region. The Gulf North unit shows signs of the recent loss of genetic variability. These proposed conservation units could be considered a generalized model of conservation for other species of cave-dwelling bats that share the same habitats.

Effect of density on growth and feeding of the crayfish Cambarellus montezumae (Saussure, 1857)

The acocil C. montezumae is a freshwater crayfish endemic to the Central Plateau of Mexico, but, in recent years, the natural population of this species has diminished considerably. In this work was investigated growth performance and feeding of this crayfish reared at high densities. A random block experimental design with two repetitions and three treatments (77, 154 and 231 crayfish/m2) was carried out. Organisms were fed every third day with 15% of their total biomass of shrimp commercial food with 25% of crude protein, and individual food consumption (IFC) was calculated. Significant differences (ANOVA, P < 0.05) were detected in final weight, absolute increase, relative rate of increase, instantaneous rate of increase, yield and survival rate between the densities, with those reared at a density of 77 organisms/m2 reaching the largest sizes. There were no-significant differences (P > 0.05) among treatments in terms of initial weight, specific growth rate and feed conversion l rate.