Aurelio Ramírez-Bautista

Parents adjust care in response to weather conditions and egg dehydration in a Neotropical glassfrog

Parental hydration of terrestrially developing eggs has evolved repeatedly among frogs and is thought to buffer embryos from environmental variation. While many anurans offer relevant opportunities to study parental care, research on how parents respond to environmental variation and offspring conditions are lacking. In this study, we investigated the interrelationships of weather, embryo hydration demands, and parental provisioning in a wild population of the glassfrog Hyalinobatrachium (‘Centrolenella’) fleischmanni in Oaxaca, Mexico. We determined whether males modify parental behavior in response to changes in weather conditions that effect embryo dehydration, how variation in both weather and parental hydration affect egg water balance and embryonic mortality, and whether parental provisioning is related to the hydration levels of egg clutches. We found that male H. fleischmanni compensate for environmental variation in offspring conditions by adjusting the frequency of parental care in response to both weather and egg dehydration. Using a male removal experiment, we examined the function of paternal care and made comparisons with previous research, finding that both the adaptive value of parental care and flexibility in parental behavior are impacted by spatial and temporal conditions. We present observations that indicate a direct conflict between providing parental care and multiple matings. In summary, this research demonstrates that the variable frequency of paternal care in H. fleischmanni is a response to the fluctuating nature of the climate and resulting hydration requirements of embryos in combination with the allocation of effort to parental care versus mating activity.

Glassfrog embryos hatch early after parental desertion

Both parental care and hatching plasticity can improve embryo survival. Research has found that parents can alter hatching time owing to a direct effect of care on embryogenesis or via forms of care that cue the hatching process. Because parental care alters conditions critical for offspring development, hatching plasticity could allow embryos to exploit variation in parental behaviour. However, this interaction of parental care and hatching plasticity remains largely unexplored. We tested the hypothesis that embryos hatch early to cope with paternal abandonment in the glassfrog Hyalinobatrachium fleischmanni (Centrolenidae). We conducted male-removal experiments in a wild population, and examined embryos response to conditions with and without fathers. Embryos hatched early when abandoned, but extended development in the egg stage when fathers continued care. Paternal care had no effect on developmental rate. Rather, hatching plasticity was due to embryos actively hatching at different developmental stages, probably in response to deteriorating conditions without fathers. Our experimental results are supported by a significant correlation between the natural timing of abandonment and hatching in an unmanipulated population. This study demonstrates that embryos can respond to conditions resulting from parental abandonment, and provides insights into how variation in care can affect selection on egg-stage adaptations.

Reproduction and sexual dimorphism of Lepidophyma sylvaticum (Squamata: Xantusiidae), a tropical night lizard from Tlanchinol, Hidalgo, Mexico

We studied reproductive characteristics of the night lizard, Lepidophyma sylvaticum (Xantusiidae) from cloud forest in Tlanchinol, Hidalgo, Mexico. Males reached sexual maturity at a snout-vent length (SVL) of 55 mm, and females reached sexual maturity at a SVL of 56 mm. Males and females were not sexually dimorphic in SVL, but males had significantly larger heads and limbs than females. Reproduction in males and females was seasonal. Testicular mass increased in July and August, reaching maximum size in September. Minimum testes size occurred in March. Follicles of females began to increase in size in September when vitellogenesis was observed. Follicles in some females increased in mass during January-March, whereas other females ovulated during that period. Late embryonic stages (35-40) were observed in July with parturition likely occurring in July and August, coincident with maximum rainfall. Litter size averaged 4.7 ± 0 .4 neonates, and was not correlated with female size. Similarities in reproductive characteristics between L. sylvaticum and other xantusiids (viviparity, long gestation period) suggest that some reproductive characteristics have a historical origin.

Sexual dimorphism and reproductive cycle in the arboreal spiny lizard Sceloporus formosus Wiegmann (Squamata: Phrynosomatidae) from central Oaxaca, México

Es bien conocido que la variacion geografica ocurre en las caracteristicas de historias de vida entre poblaciones de especies de lagartijas. Las variaciones en las caracteristicas de historias de vida encontradas en algunos estudios son posiblemente adaptaciones a las presiones del ambiente. En el suroeste de Mexico, habita la especie endemica, Sceloporus formosus la cual ha sido poco estudiada en sus caracteristicas reproductivas a traves de su intervalo de distribucion geografica. En este estudio se usaron especimenes provenientes de colecciones cientificas para describir el ciclo reproductivo de machos y hembras y dimorfismo sexual de S. formosus. En otras especies viviparas de altitudes elevadas del genero Sceloporus muestran dimorfismo, donde los machos son mas grandes que las hembras en muchas caracteristicas morfologicas; debido a esto, esperabamos que S. formosus mostrara dimorfismo sexual. Sin embargo, no encontramos dimorfismo sexual. Los machos alcanzaron la madurez sexual a menor talla (47 mm) en longitud hocico-cloaca (LHC) que las hembras (50 mm). En cuanto a la masa del higado no hubo diferencias significativas entre sexos y meses. Sin embargo, los cuerpos grasos en las hembras fueron mayores que en machos. En los machos, no hubo relaciones significativas entre log10-volumen testicular y el log10-LHC. El volumen testicular se correlaciono positivamente con la temperatura y este fue mas pequeno durante octubre, noviembre y diciembre. Para las hembras, no hubo efectos significativos del mes sobre el volumen de la gonada. La vitelogenesis ocurrio de abril a noviembre. Los foliculos vitelogenicos y el desarrollo embrionario se correlacionaron significativamente con la precipitacion (Correlacion de Pearson, r = 0.80,n=10,P = 0.0081) y el fotoperiodo (Correlacion de Pearson, r = 0.72, n = 10, P < 0.0001). El tamano de la carnada basado con el numero de embriones, se correlaciono con la LHC (Correlacion de Pearson, r = 0.82, n = 10, P = 0.0034). La masa relativa de la carnada no se correlaciono con la LHC de las hembras (Correlacion de Pearson, r = 0.43, n = 10, P = 0.2110). Este patron reproductivo otonal encontrado es tipico de especies viviparas que habitan altitudes elevadas, donde la temperatura es baja, la precipitacion y la humedad son altas. Lo que sugiere que la convergencia en los ciclos reproductivos puede estar asociada con un cambio a las condiciones ambientales imperantes en altitudes elevadas.

Oogenesis and ovarian histology in two populations of the viviparous lizard Sceloporus grammicus (Squamata: Phrynosomatidae) from the central Mexican Plateau

The annual histological changes in ovarian morphology (oogenesis, follicular atresia, and corpus luteum) are described for the Mexican lizard Sceloporus grammicus, in two populations that inhabit contrasting environments (vegetation categories, climate, precipitation, and temperature) from Hidalgo State, Mexico. Two germinal beds were situated on the dorsal surface of each ovary of this species. In both the populations, oogenesis involves two major processes: previtellogenesis and vitellogenesis. The histological changes during previtellogenesis are similar to those for other reptilian sauropsids, whereas vitellogenesis differs and the features of this last process are described for the first time. In early previtellogenesis, primary oocytes have fibrillar chromosomes and the ooplasm stains slightly. The primordial follicles are surrounded by a granulosa composed of cuboidal follicular cells. During late previtellogenesis, the oocyte had an eccentric nucleus with lamp‐brush chromosomes and multiple nucleoli. The granulosa becomes multilayered and polymorphic, containing three cell types: small, intermediate, and pyriform. The zona pellucida was homogeneous and clearly observed. In early vitellogenesis, the oocyte showed several small acidophilic granules distributed in the center and the periphery of the oocyte. As vitellogenesis progresses, the yolk platelets move toward the central area of the oocyte and they fuse to form acidophilic and homogeneous yolk. Lipid droplets were distributed irregularly in the ooplasm of the oocyte. In Zacualtipán, the results revealed a strong seasonal reproductive activity. Females had vitellogenic follicles from July to September, and pregnant females were founded from September to March. In Tizayuca, the results showed an unusual pattern of reproductive activity. Females with vitellogenic follicles and pregnant females were found throughout the year, indicating continuous reproduction. We suggest that the observed differences in reproductive activity from these populations indicate adaptative fine tuning in response to local environmental conditions. These results contribute to the knowledge of variation in vitellogenesis and reproductive strategies of this species and among spiny lizards overall. J. Morphol. 275:949–960, 2014.

Did sexually dimorphic dorsal coloration evolve by a pre-existing bias in males in the lizard Sceloporus minor?

Theory and empirical evidence indicate that male secondary sex traits can evolve by co-option of pre-existing biases in females. However, relatively few studies have explored whether male pre-existing biases could drive the evolution of traits important in male contests. Male spiny lizards (Sceloporus) are characterized by the expression of sexually dimorphic blue throat and abdominal patches. These features are revealed to conspecifics during social interactions, and variation in ventral color can predict the outcome of male contests in some species of spiny lizards. In Sceloporus minor, males in some populations also express bright blue color on the dorsal surfaces. Given the significance of blue color in intrasexual signaling in other species of Sceloporus, blue dorsal color may have evolved in S. minor by co-option of a male sensory bias for the color blue. We tested this hypothesis in a population that exhibits an ancestral phenotype for male dorsal color (brown/orange), and lacks males with bright blue dorsal coloration. Resident territorial males were presented with one of three types of intruder males manipulated in dorsal color by painting. Orange males mimicked the ancestral dorsal phenotype found at the study site; blue males resembled those from a population with the derived (blue) form of this trait; and green males represented a novel stimulus control. If blue dorsal color evolved in S. minor in part due to co-option of a male sensory bias, we predicted that resident males would exhibit either increased or decreased levels of aggression to blue intruders relative to controls. We found no difference in resident aggressive behavior across all treatments, thus failing to support the predictions of a pre-existing bias. We discuss these findings in the context of social behavior in Sceloporus, and propose directions for further study in this species.

Atypical reproductive cycles in a population of Sceloporus grammicus (Squamata: Phrynosomatidae) from the Mexican Plateau

The spiny lizard Sceloporus grammicus (Squamata: Phrynosomatidae) is a small reptile from central México and the southern United States, occurring in a wide geographic area characterized by extensive variation in topographic and climatic regimes. Genetic variation among lineages from central México is substantial, though the extent to which this variation corresponds with life-history traits remains obscure. To address part of this puzzle, we studied a population of S. grammicus from Tepeapulco, Hidalgo, México. Male-biased sexual dimorphism was extensive in this population; males were larger than females overall, and expressed proportionately larger heads and longer limbs. Minimum size at sexual maturity was similar in the sexes (males: 43 mm; females: 42 mm). In contrast to other populations from the Central Plateau, reproductive activity of males and females was synchronous. Testicular recrudescence of adult males was initiated in October–November, and maximum testis size maintained from December to July. Female reproductive activity showed no clear seasonal pattern: females had vitellogenic follicles from October to July, and pregnant females were found throughout the year. Female body size was not related to litter size. Neither male nor female gonadal mass was correlated with any abiotic environmental variable examined. Differences in reproductive characteristics among populations of S. grammicus might be indicative of plasticity in response to local environmental conditions, local adaptation, or complex gene × environment interactions. We consider these results in the context of previously studied populations of S. grammicus from the Central Plateau and elsewhere, and propose directions for future research.

Morphometric variation in island and mainland populations of two lizard species from the Pacific Coast of Mexico

BackgroundBody size exerts a strong influence on the physiology, morphology, ecology, and evolution of other life history traits in vertebrates. We compared the morphometry and allometry of two lizard species (Anolis nebulosus and Aspidoscelis lineattissima) occurring on mainland and island populations on the Pacific Coast of Mexico in order to understand the effect of an insular environment on body size and other morphometric structures.ResultsResults showed that both males and females of A. nebulosus from San Pancho Island were larger in body size than those from the mainland. Moreover, males of A. lineattissima from Cocinas Island exhibited larger forms of most measured morphometric traits than those from the mainland, whereas females from both island and mainland populations did not differ in body size or in other morphometric traits analyzed. Multivariate allometric coefficients of males and females of A. nebulosus from island and mainland populations showed a lower percentage of positive allometries than in A. lineattissima, probably because the former species is highly sedentary. Island populations of both species exhibit male-biased sexual dimorphisms in body size and size-adjusted morphometric traits. In contrast to the mainland population, morphometric comparisons of body size-adjusted traits showed that male A. lineattissima were larger than females only in head length, head width, forearm length, and tibia length, whereas in A. nebulosus, sexual dimorphism was observed just in HL.ConclusionsThis study supports the hypothesis (island rule) that vertebrates on islands are larger than those of conspecifics on the mainland. In addition, sexual dimorphism observed between males and females of both species and populations could be associated with allometric growth (positive or negative) from some morphometric structures, as well as differences in the growth rates of these organisms.

Reproductive Characteristics of Two Syntopic Whiptail Lizards, Aspidoscelis marmorata and Aspidoscelis tesselata, from the Northern Chihuahuan Desert

Abstract We studied reproductive characteristics of two syntopic whiptail lizards, Aspidoscelis marmorata and A. tesselata, inhabiting the northern Chihuahuan Desert. Reproductive characteristics studied were snout–vent length at sexual maturity, size of clutch, and volume of eggs. In A. marmorata, males and females were similar in snout–vent length, but body mass was larger in males than in females. Female A. tesselata were larger in snout-vent length and heavier than female A. marmorata. Mean size of clutch was 3.3 for A. marmorata and 3.5 for A. tesselata. Females of A. marmorata had larger volume of eggs than females of A. tesselata. Data suggest that both A. marmorata and A. tesselata respond to environmental factors of the region in different ways.

Range extension of the Giant Salamander, Pseudoeurycea gigantea (Taylor 1938) (Caudata: Pletodontidae), and some aspects of its natural history within Hidalgo state, Mexico

This study documents the most northerly known distribution of the giant salamander, Pseudoeurycea gigantea , and provides new details on aspects of its natural history based on specimens of this species collected within Hidalgo state, Mexico.