Nora R. Ibargüengoytía

Erosion of lizard diversity by climate change and altered thermal niches

Demise of the Lizards Despite pessimistic forecasts from recent studies examining the effects of global climate change on species, and observed extinctions in local geographic areas, there is little evidence so far of global-scale extinctions. Sinervo et al. (p. 894; see the Perspective by Huey et al.) find that extinctions resulting from climate change are currently reducing global lizard diversity. Climate records during the past century were synthesized with detailed surveys of Mexican species at 200 sites over the past 30 years. Temperature change has been so rapid in this region that rates of adaptation have not kept pace with climate change. The models were then extended to all families of lizards at >1000 sites across the globe, and suggest that climate change-induced extinctions are currently affecting worldwide lizard assemblages. A historical record of lizard populations in Mexico is used to parameterize models that predict global effects of climate change. It is predicted that climate change will cause species extinctions and distributional shifts in coming decades, but data to validate these predictions are relatively scarce. Here, we compare recent and historical surveys for 48 Mexican lizard species at 200 sites. Since 1975, 12% of local populations have gone extinct. We verified physiological models of extinction risk with observed local extinctions and extended projections worldwide. Since 1975, we estimate that 4% of local populations have gone extinct worldwide, but by 2080 local extinctions are projected to reach 39% worldwide, and species extinctions may reach 20%. Global extinction projections were validated with local extinctions observed from 1975 to 2009 for regional biotas on four other continents, suggesting that lizards have already crossed a threshold for extinctions caused by climate change.

Reproductive biology and sexual dimorphism of a high-altitude population of the viviparous lizard Phymaturus punae from the Andes in Argentina

Phymaturus punae is a viviparous lizard endemic to the Provincial Reserve San Guillermo, San Juan (Argentina). We present the first life history data of P. punae , belonging to an interesting genus adapted to cold climates. Females reach sexual maturity at 80.6 mm, and males at 84.4 mm snout-vent length. There is sexual dimorphism represented by larger and more robust males, but females show a wider body and a proportionally greater interlimb length than males. In males, spermatozoa become abundant in both testes and epididymi in mid-summer. Vitellogenic and pregnant females occurred simultaneously in late spring and mid-summer indicating a biennial reproductive cycle.

Asynchronous spermatogenesis and biennial female cycle of the viviparous lizard Phymaturus antofagastensis (Liolaemidae): reproductive responses to high altitudes and temperate climate of Catamarca, Argentina

This paper studies minimum SVL at sexual maturity, sexual dimorphism, operational sex ratio, male and female reproductive cycles, and litter size of viviparous Phymaturus antofagastensis, a species living at high altitude in the temperate climate of Catamarca, Argentina. Males reached sexual maturity at 90 mm, and females at 79 mm. Adult males attained significantly larger body size and head width than adult females. Histological analysis showed asynchrony in spermatogenesis timing among males and spermatozoa storage in epididymis throughout the reproductive season (spring to early autumn). Females showed a biennial reproductive cycle taking at least one activity season to perform either vitellogenesis or pregnancy. Brood size resulted in two offspring, a condition similar to other species of the genus, with births occurring in late summer. The reproductive cycle of Phymaturus antofagastensis shows a new response in males and females to harsh environments characterized by short activity seasons, long hibernation periods and large daily and seasonal thermal fluctuations.

Phymaturus of Patagonia, Argentina: Reproductive Biology of Phymaturus zapalensis (Liolaemidae) and a Comparison of Sexual Dimorphism within the Genus

Abstract Lizards of the viviparous genus Phymaturus inhabit regions in which a significant proportion of the year is unsuitable for growth and reproduction. All Phymaturus studied have shown biennial female reproductive cycles. We studied the reproductive biology of Phymaturus zapalensis, which lives on rocky outcrops in cold and arid environments of Patagonia, Argentina. Male and female reproductive cycles, mean annual reproductive output, and sexual dimorphism were analyzed. Additionally, new dimorphic traits of Phymaturus antofagastensis and Phymaturus tenebrosus were compared with published data. The female reproductive cycle of P. zapalensis is annual-biennial (because of skipping a year of reproduction), and synchronous with the annual male reproductive cycle. In midspring, males show spermatozoa in epididymis, and females have enlarged follicles, characteristic of imminent ovulation. The presence of 45% of the adult females with oocytes smaller than 4 mm, in all months of capture except October, suggests a year of skipped reproduction. Female P. zapalensis had greater SVL and a relative larger interlimb length than males. Males exhibited relatively greater head width, neck width, and diameter of front and hind legs. Our data indicate that the potential for annual reproduction exists in this biennial breeding genus. The capability of P. zapalensis to perform either an annual or biennial reproductive cycle, instead of the characteristic biennial cycle of the genus, could be the result of a longer activity season, higher temperatures during spring, summer, and autumn months, together with a high-energy omnivorous diet.

Growth and age of the southernmost distributed gecko of the world (Homonota darwini) studied by skeletochronology

Homonota darwini is the southernmost distributed gekkonid species of the world, as it can be found in South America from 35° to 52°S. Age and growth of H. darwini were studied using skeletochronology on diaphyseal femoral cross-sections. Individual ages were assessed after estimating the resorbed rings in relation to snout-vent length (SVL). SVL and age showed a sigmoidal relationship and growth rates showed a shift from premature growth to mature breeding when sexual maturity is achieved. The model indicates that sexual maturity in H. darwini is reached at five years in females and nine in males. Species longevity is estimated to be 17 years, which corresponds to a k-selected trait of late maturity and long life expectancy. Once sexual maturity is achieved, size is a poor indicator of age in this species. These results are discussed in terms of behavioural and physiological adaptations of this species to the strong environmental pressures of the Patagonian steppe. Our results also support the hypothesis that daytime burrow temperatures, which are similar to body temperatures recorded in diurnal lizard species, meet the physiological growth requirements of nocturnal lizard species.

Age and growth of the Patagonian lizard Phymaturus patagonicus

The growth dynamics of Phymaturus patagonicus, a diurnal, herbivorous and viviparous lizard from the Argentinean Patagonian steppe, was studied using eight juveniles (two born in the laboratory), 11 adult females and eight adult males. Histological cross sections of femoral bones were analysed to determine if individuals show osseous growth marks and if these marks provide useful age estimates. Individual ages were assessed after estimating the reabsorbed rings in relation to snout-vent length. There was a strong relationship between body length and estimated age, modelled by a sigmoidal curve. Sexual maturity was found to be reached at seven years in females and nine in males and the maximum life span was estimated to be 16 years. No difference in body length was observed between the same-age females and males. We postulate that severe environments such as the north Patagonian steppe play a significant role in the selection of not only modes of reproduction but also delayed maturity and prolonged reproductive cycles, a combination that results in low fecundity.

Thermal effects on locomotion in the nocturnal gecko Homonota darwini (Gekkonidae)

Nocturnal lizards show a complex adaptation to environmental temperature. They obtain heat from the substratum, using daytime for performing physiological functions inside thermally suitable shelters, and night-time which involves locomotion and loss of heat for capturing prey. Homonota darwini, the southernmost geckonid in the world, is a small nocturnal insectivorous gecko that occurs in saxicolous habitats of Patagonia, Argentina. Geckos were captured by hand during the day on a rocky hill near Bariloche (Rio Negro, Argentina) in spring and summer. All the geckos were active during daytime and had good limb mobility with a median body temperature of 23 ◦ C. Body temperatures showed a direct dependence on the temperature of the roof of the shelter and on the air temperature. Geckos were made to run on a horizontal track and running speed was measured in two experiments: long runs (1 m) and sprint runs (0.20 m) during the day (diurnal) and at night (nocturnal). Speed was significantly greater in sprints than in long runs and speed increased with body temperature, reaching a maximum at a body temperature of 22 ◦ C. Thus, we conclude that, although the low temperatures of Patagonia impose heavy constraints on the physiological performance of Homonota darwini, they have a peculiar arrangement of mechanical and biochemical abilities which allows for resource acquisition at night, using cryptic habits and short sprint runs.

SIGNS OF PARENTAL BEHAVIOR IN LIOLAEMUS ELONGATUS (SAURIA: LIOLAEMIDAE) OF NEUQUÉN, ARGENTINA

Abstract Parental care in reptiles has been correlated with cold climates and harsh environments. We investigated whether behavioral patterns indicating parental care occurred in the lizard, Liolaemus elongatus, a viviparous species found on rocky outcrops of the Argentinean Patagonia. Five pregnant females were captured during the austral summer and brought to the laboratory for observations. The females were filmed for short periods of time during six days after the birth of their young. During that time, the mothers and offspring were presented with three predatory stimuli, a Diplolaemus sexcinctus, a male Liolaemus elongatus, and a stuffed hawk, Elanus leucurus. Their responses were recorded as well as the distance between mothers and offspring during the experiments and when no stimuli were presented. Except for one female, mothers constructed burrows in which the neonates were born. Mothers and their offspring occupied the same shelter for the whole period of observation. When presented with predatory stimuli, females seemed to choose between remaining near or on top of the burrow with the young inside, or moving away from it. When the offspring were out of the burrow, a female occasionally covered a neonate, forming a bridge over it, particularly when threatened. Mothers showed individual variations in the way they responded to the different stimuli that were presented.

Consequences of volcanic ash deposition on the locomotor performance of the Phymaturus spectabilis lizard from Patagonia, Argentina

The locomotor performance of lizards depends on their morphological and physiological adaptations to the habitat. However, when the habitat changes dramatically, for example, by a volcanic eruption, the performance of lizards may be affected. We registered the vegetation cover, the surface covered by ash, the presence of crevices suitable for Phymaturus and the rocks slopes to analyze the effects of ash accumulation produced by the eruption of Puyehue-Cordon Caulle volcanic complex on microhabitat use and availability of the Phymaturus spectabilis lizard. In addition, we studied the effect of ashes and slope on the locomotor performance of P. spectabilis by registering the maximum speed in sprint runs and long runs under four different treatments (cork and on the level, ashes and on the level, cork and slope, and ashes and slope). P. spectabilis selected microhabitats unvegetated, with crevices and steep slopes. Regarding locomotor performance, the speed of lizards was negatively affected by the presence of ash only in sprint runs on the level and in long runs with slope. The slope had a negative impact on the speed in all the treatments. These results show that the presence of volcanic ashes in the substrate might have affected the locomotor performance of the lizards, especially in long runs, and hence, the interaction of individuals with the environment, that is, escaping from predators and social behavior.

Asynchronic steroid activity of Leydig and Sertoli cells related to spermatogenic and testosterone cycle in Phymaturus antofagastensis

The severe environments where Phymaturus lizards inhabit in the Andes highlands and in Patagonia, Argentina, impose restrictions on their reproduction, offering a framework for the development of life history strategies to overcome hard weather conditions. Among them, prolonged female cycles, asynchrony between sexes in receptivity, and sperm storage in males, were described. Asynchrony in the reproductive timing between males and females is a consequence of different energy requirements for gametogenesis, and often imply the existence of cellular mechanisms to enhance fertilization, such as the asynchronic steroid synthesis between testicular compartments, allowing gametogenesis independently of mating. In the present study ultrastructural and hormone assays were combined for the first time in liolaemids. Specifically, morphological features of steroid activity in Leydig and Sertoli cells, and serum testosterone concentrations have been studied in the lizard Phymaturus antofagastensis. Leydig and Sertoli cells presented morphological features characteristic of steroid synthesis during the spermatogenesis, and evident asynchronic steroid production between testicular compartments. Active Sertoli cells and inactive Leydig cells were observed in spring and autumn, while in mid-summer their steroid activity was synchronic in coincidence with maximal abundance of spermatozoa in epididymis. Serum testosterone concentration was at its maximum in mid-summer (126-230 ng ml(-1)), and minimum in late spring (4-24 ng ml(-1)) and early autumn (2-17 ng ml(-1)). In view of these results, P. antofagastensis males show an original approach to adjust their reproductive activity to physiological and environmental constraints at high latitudes and altitudes in the Andean highlands of Argentina.