Female Reproductive Cycles of Phrynocephalus przewalskii (Lacertilia:Agamidae) in the Tengger Desert,China

The timing of reproduction can significantly affect an offspring＇s fitness, thereby also influencing the fitness of the parents, especially in species inhabiting extreme environments, such as deserts. Female reproductive cycles in Phrynocephalus przewalskii were studied from April to September 2008. Significant cycles of gonadal volume were found in all studied populations and the cycles were similar among the various populations. Females began vitellogenesis in April and contained oviductal eggs form May to June. Gonad volume decreased significantly in July and reached minimum volume from August to September. The follicular growth was negatively correlated with increasing precipitation and temperature in all populations. Hatching occurs during summer and early fall, when most of the annual rainfall occurs. Mean clutch size based on all populations was 2.7 ± 0.9 SE （n = 71）.

Sexual Dimorphism of Head Size in Phrynocephalus przewalskii: Testing the Food Niche Divergence Hypothesis

Sexual size dimorphism （SSD） is a general phenomenon in lizards, and can evolve through sexual selection or natural selection. But natural selection, which was thought to operate mainly through reducing the competition be- tween the two sexes （niche divergence hypothesis）, gave rise to a lot of controversy. We tested the niche divergence hypothesis in the toad-headed lizard Phrynocephalus przewalskii by comparing diet composition and prey sizes between males and females. The species was found to be sexual dimorphic, with males having relatively larger snout-vent length, head width, head length, and tail length, while females have relatively larger abdomen length. Based on analysis of 93 studied stomachs, a total of 1359 prey items were identified. The most common prey items were formicid, lygaeid and tenebrionid. The two sexes did not differ in the relative proportions of prey size categories they consumed and the dietary overlap based on prey species was high （O = 0.989）. In addition, the meal size, the volume or any maximal dimension of the largest prey item in the stomach was not explained by the sexes. According to our results, food niche divergence might not play an important role in the SSD evolution ofP. przewalskii.

Geographic Variation in Clutch and Egg Size for the Lizard Phrynocephalus przewalskii(Squamata:Agamidae)

In order to tease apart proximate vs. ultimate sources of variation in reproductive strategy, studies have increasingly focused on populations rather than species as the unit of interest. The reproductive parameters of Phrynocephalus przewalskii （Agamidae） in different populations within the same phylogenetic clade were compared in this study. Female SVL, clutch size, egg volume and clutch volume varied significantly among populations. With increase in latitude, clutch size increased, while egg size decreased. Relatively fewer but larger eggs were produced with increasing of population density. Food availability had positive effects on clutch size, but no effect on egg size. Our result indicated that latitude, food availability and population density may be the proximate factors affecting the reproductive parameters ofP. przewalskii.

Effects of Thermal and Hydric Conditions on Egg Incubation and Hatchling Phenotypes in Two Phrynocephalus Lizards

Flexible-shelled eggs of the lizards Phrynocephalus przewalskii and P. versicolor were incubated under different thermal and hydric conditions to elicit the effects of incubation environment on hatching success, embryonic development and duration as well as hatchling phenotypes. Embryogenesis of the two species was not sensitive to changes in the hydric environment except P. przewalskii incubated in 30°C group. Temperature significantly altered the duration of embryogenesis, with cooler temperatures leading to a longer incubation period. Hatching success was greater at 26 and 30°C than at 34°C. The hatchlings incubated at 26 and 30°C had longer snout-vent length, larger body mass, and better locomotor performance than those incubated at 34°C. Compared to P. przewalskii, P. versicolor had a shorter incubation period and yielded smaller hatchlings, which then had a higher survival rate in cooler and drier habitats. We conclude that an incubation temperature of 30°C would produce the best balance among developmental rate, hatching success, and post-hatching performance. We speculate that the upper temperature limit for incubation of P. versicolor eggs may be slightly higher than 34°C.

Desertification Drives the Shift in Egg Size-Number Trade-Off in an Agamid Lizard

Desertification is a serious ecological problem leading to significant biodiversity loss,but how desertification drives shifts in life history and fitness of animals remains understudied.To clarify whether habitat desertification causes shifts in life history strategies,we compared ecological factors and reproductive traits of Phrynocephalus przewalskii from three different desertification habitats-fixed dune,semi-fixed dune and mobile dune of a semi-arid region of Inner Mongolia,at the eastern edge of Hobq Desert,China.Our results showed a significant shift in the egg size-number trade-off of P.przewalskii in response to desertification,with lizards from the mobile dune habitat producing smaller clutches of larger eggs than lizards from the fixed and semi-fixed dune habitats.This life history shift is likely adaptive and driven by abiotic factors(temperature and precipitation)rather than biotic factors(food availability and lizard population density).Our study demonstrates that habitat desertification drives the shift in egg size-number trade-off in a lizard and highlights the importance of exploring the life history responses of animals to habitat desertification as well as to other traditionally well-studied factors like temperature,especially in the context of future global clima te change.

荒漠沙蜥松果眼和侧眼的比较

荒漠沙蜥松果眼和侧眼的基本结构相似,均由角膜、晶体、玻璃体和视网膜组成。但松果眼的结构较侧眼简单,处于种系发生的低级阶段,只能感光,不能视物。