Microgeographic variation in body condition of three Mexican garter snakes in central Mexico.

BACKGROUND: Geographic variation in body size and condition can reveal differential local adaptation to resource availability or climatic factors. Body size and condition are related to fitness in garter snakes (Thamnophis), thus good body condition may increase survival, fecundity in females, and mating success in males. Phylogenetically related species in sympatry are predicted to exhibit similar body condition when they experience similar environmental conditions. We focused on interspecific and geographical variation in body size and condition in three sympatric Mexican garter snakes from the highlands of Central Mexico. METHODS: We assessed SVL, mass, and body condition (obtained from Major axis linear regression of ln-transformed body mass on ln-transformed SVL) in adults and juveniles of both sexes of Thamnophis eques, T. melanogaster, and T. scalaris sampled at different locations and ranges from 3-11 years over a 20-year period. RESULTS: We provide a heterogeneous pattern of sexual and ontogenic reproductive status variations of body size and condition among local populations. Each garter snake species shows locations with good and poor body condition; juvenile snakes show similar body condition between populations, adults show varying body condition between populations, and adults also show sex differences in body condition. We discuss variations in body condition as possibly related to the snakes' life cycle differences.

Non-marine ostracodes from highland lakes in East-central Mexico / Ostrácodos no-marinos de lagos en el altiplano este-centro de México

The ostracode fauna of the neartic-neotropical transitional zone has remained poorly known until this study. Ten ostracode species inhabit ten highland lakes (five maar lakes (phreatic/phreato-magmatic explosion origin), one volcanic-tectonic lake, three natural dams and one man-made dam) in East-central Mexico. Surface sediments from the deepest part and the littoral zone from all studied lakes were collected. Environmental variables (pH, temperature, dissolved oxygen, conductivity, TDS) were measured in situ and parallel water samples for chemical analysis were collected for habitat description. Widely distributed species in the study area (≥5 lakes) include Cypridopsis vidua, Darwinula stevensoni and Eucandona cf. patzcuaro. Limnocytherina axalapasco is an endemic species and was collected in three maar lakes and in one man-made dam. Rare species included: Chlamydotheca arcuata?, Fabaeformiscandona acuminata?, Ilyocypris gibba?, Limnocythere friabilis?, Potamocypris smaragdina? and Potamocypris unicaudata?. Highest species richness (6 spp.) was found in the large and shallow Lake Metztitlán (2.6km², 5.5m deep), with the lake water type HCO3->>SO4²->Cl--- Ca2+>Na+>Mg2+. The rest of studied lakes (<63m, <27km²) had not more than three species. For instance, only two ostracode species were collected in Lake Alchichica, which is the largest, deepest and most saline studied maar lake. Rev. Biol. Trop. 63 (2): 401-425. Epub 2015 June 01.

La fauna de ostrácodos de la zona de transición néartica-neotropical ha sido poco estudiada hasta este estudio. En el este-centro de México, habitan diez especies de ostrácodos en diez lagos: cinco lagos maar (originados por explosiones freáticas/freato-magmáticas), un lago volcánico-tectónico, tres embalses naturales y un embalse artificial. De la parte más profunda y de las zonas litorales de todos los lagos estudiados se recolectaron sedimentos superficiales para el análisis de ostrácodos. También se midieron in situ las variables ambientales: pH, temperatura, oxígeno disuelto, conductividad, SDT, además se recolectaron muestras de agua paralelas para análisis químico con el objetivo de describir el hábitat. Especies con una amplia distribución en el área de estudio (≥5 lagos) incluyen: Cypridopsis vidua, Darwinula stevensoni y Eucandona cf. patzcuaro. Limnocytherina axalapasco es una especie endémica y fue recolectada en tres lagos maar y en el embalse artificial. Especies raras incluyeron: Chlamydotheca arcuata?, Fabaeformiscandona acuminata?, Ilyocypris gibba?, Limnocythere friabilis?, Potamocypris smaragdina? y Potamocypris unicaudata? La riqueza de especies más alta (6 spp.) se encontró en el lago más extenso y somero, lago Metztitlán (2.6km², 5.5m de profundidad), con el tipo de agua HCO3->>SO4²->Cl--- Ca2+>Na+>Mg2+. El resto de lagos estudiados (<63m, <27km²) presentaron no más de tres especies. Por ejemplo, solamente dos especies de ostrácodos fueron recolectadas en el lago Alchichica, el cual es el más extenso, profundo y salino entre los lagos maar estudiados.