Felipe Rodríguez-Romero

DEMOGRAPHY OF A SEMELPAROUS, HIGH-ELEVATION POPULATION OF SCELOPORUS BICANTHALIS (LACERTILIA: PHRYNOSOMATIDAE) FROM THE NEVADO DE TOLUCA VOLCANO, MEXICO

Abstract We studied demography of a population of viviparous lizard, Sceloporus bicanthalis, from Nevado de Toluca Volcano, Mexico, using mark-recapture methods. Age structure of this population varied seasonally due to an increase in number of juveniles over summer, although neonates were observed in every month. Estimated average density was 304 individuals/ha. Snout-vent length at sexual maturity in viviparous S. bicanthalis was 31 mm in males and 32 mm in females. Males survived longer than females, with an expected lifespan of 15 months, compared to 8 months for females. Net reproductive rate of this population was 1, suggesting it was at equilibrium, while generation time was 7 months. This high-elevation population has a semelparous life cycle.

The Differential Effect of Tail Autotomy on Sprint Performance between the Sexes in the Lizard Uta stansburiana

Abstract Autotomy of an appendage, especially the tail in lizards, can aid in escape from predators, but that assistance comes with associated costs. In previous studies, decreases in sprint performance often followed tail loss in lizards, and potential sexual differences following tail autotomy can provide evidence for the possible influence of sexual selection on performance in lizards. We measured the impact of tail autotomy on sprint performance in the lizard Uta stansburiana, a species that has frequent natural tail loss. Sprint performance was measured using both maximal sprint speed and average stride length. We examined the impacts separately for each sex, as this species is molded strongly by sexual selection, and tail autotomy is known to affect the social status of male and female subadult U. stansburiana differently. To check for sexual differences in sprint performance, we assessed both sexes with intact tails. Neither sprint speed nor stride length significantly differed between the sexes. Following tail loss, male performance was not affected; individuals maintained their previous maximal sprint speed and average stride length. However, females significantly decreased both maximal sprint speed and average stride length following tail autotomy. We suggest that tailless males maintain high speeds to escape predators because of greater conspicuousness due to sexual dimorphism and behavior, as well as for repulsion of rivals from their territories. Postautotomy females may adopt an alternate social role that does not require their prior sprint speeds. Sexual selection may have advanced this sexual difference in sprint performance after tail autotomy.

Correlaciones Morfológicas entre la Forma de la Cabeza, Dieta y uso de Hábitat de Algunos Sceloporus de México: Un Análisis Cuantitativo

La relacion entre los caracteres morfologicos y la ecologia de los organismos permite deducir respuestas adaptativas. Estas adaptaciones son el resultado de presiones selectivas que actuan sobre los organismos, asi como el tipo de presa que consumen o el ambiente en el que se encuentran. De esta manera, los organismos exhiben morfologias que les permiten explotar los recursos disponibles. Sceloporus es un grupo de lagartijas altamente diverso en Norteamerica ademas de encontrarse en diversos habitats, lo que lo hace un modelo optimo para probar hipotesis adaptativas y evolutivas. El objetivo fue evaluar si existen diferencias morfologicas en la cabeza de algunas especies de Sceloporus y determinar si dicha morfologia surge como una respuesta adaptativa al tipo de presa o al uso de habitat. Para ello, se tomaron ocho variables morfometricas de la cabeza de 20 especies de este genero y que se distribuyen en Mexico. Los datos de dieta y uso de habitat se obtuvieron de literatura y se correlacionaron con los analsis morfologicos de este estudio. Los resultados indican una clara diferencia entre especies con respecto a cinco de ocho variables medidas, entre ellas se observo el alto de la cabeza, hocico, mandibula, sinfisis mandibular y proceso retroarticular. Ademas, se obtuvo que el ancho y alto de la cabeza, se encuentran relacionados con el tipo de presa que las lagartijas consumen, y unicamente el alto de la cabeza, se correlaciona con el uso de habitat. Con base en los resultados, se propone que la morfologia de la cabeza de las lagartijas que se analizaron, esta siendo moldeada por el tipo de presas que consumen y no por el ambiente, tal como se ha observado en otros lacertilios.

Taxonomic Assessment of the Subspecific Status of Phrynosoma orbiculare (Sauria: Phrynosomatidae) In the Southern Portion of Its Distribution

Abstract Phrynosoma orbiculare is an endemic species of lizards in Mexico and is distributed from the northern part of the country to the central highlands. This species is found in open areas among scrubs, grasses, yuccas, and herbaceous plants. In our study, we performed two multivariate analyses (principal components and discriminant functions) to examine morphological and geographic variation among populations of P. orbiculare at the edge of the southern distribution of the species. Our assessment was to determine the taxonomic status of the subspecies Phrynosoma orbiculare orbiculare, P. o. cortezii, and P. o. boucardi described for this geographic zone. The analyses employed 10 informative diagnostic traits from digitalized images. Our results confirm only two subspecies, P. o. orbiculare and P. o. cortezii, in the study area. In addition, two new localities for the distribution of the species have been included (Nopalillo, Hidalgo, and Amealco, Queretaro). Moreover, the morphometrics of the organisms from new localities revealed that all individuals were positioned in the P. o. cortezii group and that the distribution of this subspecies extends west of the original records. We propose that the two populations reported as P. o. boucardi can be renamed as P. o. cortezii.

Relative importance of reproductive life-history paths in one population of the lizard Sceloporus grammicus

Life cycles of living organisms are composed of distinct sub-cycles that represent alternative life-history paths with differential impact on fitness. We identified three reproductive life-history paths (referred here as loops) in the life cycle of one population of the viviparous lizard Sceloporus grammicus .W e evaluated the relative importance of each one of these reproductive paths for the population fitness of these lizards during a 5-year period. The first path corresponded to early reproduction and included survival to maturity and early fecundity. The second path was late reproduction loop and included survival to larger adult sizes with the corresponding fecundity rate. The third was composed of those individuals skipping the small adult stage within a single year, reaching larger sizes early in life with their corresponding larger litters (fast growth loop). To examine the potential effects of environmental factors on the relative contribution of these alternative life-history paths to fitness, we estimated stage-specific survival and growth as functions of annual temperature and rainfall. Using these estimates of vital rates we constructed annual population projection matrices. Then, using demographic elasticities and loop analysis, we calculated the relative contribution of each of the three reproductive paths to the population growth rates. Our results showed that the early reproduction loop is the path with the greatest relative contribution to the population growth rate in most years. However, increases in environmental temperature resulted in higher population growth rates and in greater contribution of the fast growth path to the overall fitness of these lizards.

Rediscovered Population of Mexican Plateau Spotted Whiptail Lizard, Aspidoscelis septemvittata (Teiidae), from México, D.F.

ABSTRACT. Multiple surveys carried out by herpetologists in México, D.F., during the 1980s failed to find specimens of Aspidoscelis septemvitatta (Squamata: Teiidae). However, 10 specimens were recently collected to the east of México, D.F., inside a protected area, Sierra de Santa Catarina. The Sierra de Santa Catarina has been heavily modified by human activity and habitation. Morphological and natural history information about the specimens are presented, as well as notes on locality.