THE EVOLUTION OF MATERNAL INVESTMENT IN LIZARDS: AN EXPERIMENTAL AND COMPARATIVE ANALYSIS OF EGG SIZE AND ITS EFFECTS ON OFFSPRING PERFORMANCE

I used comparative and experimental analysis of egg size in a Sceloporus lizard to examine a fundamental tenet of life-history theory: the presumed trade-offs among offspring number, offspring size, and performance traits related to offspring size that are likely to influence fitness. I analyzed latitudinal and elevational patterns of egg life-history characteristics among populations and experimentally manipulated egg size and hatchling size by removing yolk from the eggs to examine the causal bases of population differences in offspring traits. Mean clutch size among populations increased to the north (seven vs. 12 eggs/clutch, California vs. Washington), whereas egg size decreased (0.65 g vs. 0.40 g). The elevational patterns in southern California paralleled the latitudinal trends. Several offspring life-history traits that are correlated with egg size also varied geographically; these traits included incubation time, hatchling size, growth rate, and hatchling sprint performance. Hatchling viability of experimentally reduced eggs was remarkably high (~70%), even when up to 50% of the yolk was removed. The experimentally reduced eggs and hatchlings demonstrated the degree to which size influences each of the offspring life-history traits considered. Northern eggs hatched sooner, in part because of their small size. Though growth rate is allometrically related to size within each population (i.e., smaller hatchlings grow faster on a mass-specific basis), population differences in growth rate, as measured in the laboratory, are likely to reflect genetic differentiation in the underlying physiology of growth. Moreover, smaller juveniles, because of experimental reduction, had slower sprint speeds than larger juveniles. The slower sprint speed of hatchlings from Washington compared to hatchlings from California is thus largely due to the fact that eggs are smaller in the Washington population. These results provide a basis for interpreting the evolutionary divergence of the suite of traits involved in the evolution of maternal investment per offspring in lizards. For example, evolutionary divergence in some offspring traits functionally related to size (e.g., sprint speed) may be constrained, relative to traits that are determined by other aspects of development or physiology (e.g., growth). I also discuss issues relating to the evolution of maternal investment that could be tested in laboratory and natural populations using experimentally reduced offspring.     

Thermal sensitivity of growth rate in hatchling Sceloporus lizards: environmental,behavioral and genetic aspects

Summary To investigate the physiological, behavioral, and genetic contributions to growth rate, we studied the thermal sensitivity of growth rate in hatchlings of the iguanid lizards Sceloporus occidentalis and S. graciosus in the laboratory. We used a cycling thermal regime patterned after thermal environments found in nature. Growth rates increased with duration of access to radiant heat. Thus, variation in the thermal environment can cause phenotypic variation in growth rate and hence body size. The two species differed in both the magnitude and thermal sensitivity of growth rate, and these differences were associated with differences in behavioral thermoregulation. Thus, growth is determined interactively by both behavior and physiology. We found evidence of among-family variation in the growth rates of S. occidentalis, suggesting that growth rate has the genetic potential to evolve. In S. occidentalis, both growth rate and egg size affected body size of hatchlings at several weeks of age. In turn, hatchling size may affect fitness: for example, larger S. occidentalis hatchlings had higher sprint speeds and may therefore be more adept at capturing prey or evading predators. Our results demonstrate that growth rate has genetic, behavioral, and physiological components, and that the resulting effects on body size may have important consequences for ecological performance e.g., sprint speed.     

安徽宿州山地麻蜥卵孵化温度效应

用3个恒定温度(27、30、33℃)和波动温度(14.0～37.5℃)孵化山地麻蜥(Eremias brenchleyi)卵。结果表明,各温度处理下卵孵化成功率差异不显著,但温度对孵化期、孵出幼体表型特征及疾跑速度有显著影响;27、30℃和波动温度下孵出幼体的SVL、重量及躯干干重比33℃的要大,33℃孵出幼体的运动能力比其他3个温度处理弱。波动温度处理下山地麻蜥卵虽短期经历潜在致死的极端温度,但对孵化成功率、孵出幼体表型特征和运动表现均无负效应。     

Sprint Speeds of Juvenile Scorpions: Among Family Differences and Parent Offspring Correlations

Sprinting from predators is an important part of the defensive repertoire of some scorpions. This study examined sprint speed in juvenile scorpions and its relation to sprint speed of the mothers. Sprint speeds of juvenile scorpions, Centruroides vittatus, were determined by repeated trials on a small racetrack. Speeds were repeatable across trials within individuals and differed among individuals. There were marked among family differences in juvenile sprint speeds. Juvenile sprint speeds were correlated with maternal sprint speeds. Although the effect of common maternal environment may inflate the measures of heritability to an unknown extent, these results suggest that sprint may respond to natural selection and there is an underlying genetic basis to observed performance differences among scorpions.     

Potential ‘costs of reproduction’ in a skink: Inter‐ and intrapopulational variation

Reproductive costs are important determinants of reproductive effort in squamate reptiles. Consequently, differences in costs of reproduction between populations of geographically or climatically widespread species are likely to result in different patterns of reproductive effort. In the present study, the effect of pregnancy on sprint speed was examined in a small viviparous skink, Niveoscincus ocellatus (Gray 1845), from two populations at the climatic extremes of its distribution. Decreased sprint speed has the potential to be an important cost of reproduction in this species, through a reduced ability to avoid predation and/or decreased foraging efficiency. Lizards inhabiting the colder site were larger than those from the warmer site and, contrary to predictions from life history theory, had a higher reproductive effort. In both populations, sprint speed was lower in pregnant lizards than in either the same individuals after birth or non‐pregnant control lizards. Within each population, sprint speed was unrelated to the level of reproductive effort of the female in terms of either absolute mass of the reproductive burden or the burden relative to her post‐partum body mass. However, within each population, the mass of the clutch that an individual female was carrying relative to snout–vent length was an important determinant of her sprint speed while pregnant. Thus, within each population, a relatively high reproductive burden may potentially increase costs of reproduction in this species. Despite this relationship and predictions from life history theory suggesting that annual reproductive effort will be lower in populations with a large body size and delayed maturity, it is suggested that a higher reproductive effort at the cold site is possible because they have a higher absolute sprint speed because of their larger size and a relatively higher abundance of cover at the cold site, and differences in predation pressure may alter selective pressures on reproductive investment.     

Functional and ecological relevance of intraspecific variation in body size and shape in the lizard Podarcis melisellensis (Lacertidae)

Within populations, individual animals may vary considerably in morphology and ecology. The degree to which variation in morphology is related to ecological variation within a population remains largely unexplored. We investigated whether variation in body size and shape among sexes and age classes of the lizard Podarcis melisellensis translates in differential whole-animal performance (sprint speed, bite force), escape and prey attack behaviour in the field, microhabitat use and diet. Male and female adult lizards differed significantly in body size and head and limb proportions. These morphological differences were reflected in differences in bite strength, but not in sprint speed. Accordingly, field measurements of escape behaviour and prey attack speed did not differ between the sexes, but males ate larger, harder and faster prey than females. In addition to differences in body size, juveniles diverged from adults in relative limb and head dimensions. These shape differences may explain the relatively high sprint and bite capacities of juvenile lizards. Ontogenetic variation in morphology and performance is strongly reflected in the behaviour and ecology in the field, with juveniles differing from adults in aspects of their microhabitat use, escape behaviour and diet.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 251–264.     

Effects of constant and fluctuating temperatures on egg survival and hatchling traits in the northern grass lizard (Takydromus septentrionalis, Lacertidae)

To understand how nest temperatures influence phenotypic traits of reptilian hatchlings, the effects of fluctuating temperature on hatchling traits must be known. Most investigations, however, have only considered the effects of constant temperatures. We incubated eggs of Takydromus septentrionalis (Lacertidae) at constant (24 degrees C, 27 degrees C, 30 degrees C and 33 degrees C) and fluctuating temperatures to determine the effects of these thermal regimes on incubation duration, hatching success and hatchling traits (morphology and locomotor performance). Hatching success at 24 degrees C and 27 degrees C was higher, and hatchlings derived from these two temperatures were larger and performed better than their counterparts from 30 degrees C and 33 degrees C. Eggs incubated at fluctuating temperatures exhibited surprisingly high hatching success and also produced large and well-performed hatchlings in spite of the extremely wide range of temperatures (11.6-36.2 degrees C) they experienced. This means that exposure of eggs to adversely low or high temperatures for short periods does not increase embryonic mortality. The variance of fluctuating temperatures affected hatchling morphology and locomotor performance more evidently than did the mean of the temperatures in this case. The head size and sprint speed of the hatchlings increased with increasing variances of fluctuating temperatures. These results suggest that thermal variances significantly affect embryonic development and phenotypic traits of hatchling reptiles and are therefore ecologically meaningful.     

Swimming performance of hatchling green turtles is affected by incubation temperature

In an experiment repeated for two separate years, incubation temperature was found to affect the body size and swimming performance of hatchling green turtles (Chelonia mydas). In the first year, hatchlings from eggs incubated at 26°C were larger in size than hatchlings from 28 and 30°C, whilst in the second year hatchlings from 25.5°C were similar in size to hatchings from 30°C. Clutch of origin influenced the size of hatchlings at all incubation temperatures even when differences in egg size were taken into account. In laboratory measurements of swimming performance, in seawater at 28°C, hatchlings from eggs incubated at 25.5 and 26°C had a lower stroke rate frequency and lower force output than hatchlings from 28 and 30°C. These differences appeared to be caused by the muscles of hatchlings from cooler temperatures fatiguing at a faster rate. Clutch of origin did not influence swimming performance. This finding that hatchling males incubated at lower temperature had reduced swimming ability may affect their survival whilst running the gauntlet of predators in shallow near-shore waters, prior to reaching the relative safety of the open sea.     

Beyond black and white: divergent behaviour and performance in three rapidly evolving lizard species at White Sands

Determining which traits enable organisms to colonize and persist in new environments is key to understanding adaptation and ecological speciation. New environments can present novel selective pressures on colonists' morphology, behaviour, and performance, collectively referred to as ecomorphology. To investigate ecomorphological change during adaptation and incipient ecological speciation, we measured differences in morphology (body shape and size), behaviour (startle response), and performance (sprint speed) in three New Mexican lizard species: Holbrookia maculata, Sceloporus undulatus, and Aspidoscelis inornata. Each species is represented by dark morphs, cryptic on the brown adobe soils of the Chihuahuan Desert, and white morphs, cryptic on the gypsum substrate of White Sands. For each species, we then determined the effects of morphology and startle response on sprint speed on matched and mismatched substrate. For two of the three species, white morphs had larger body size and longer limbs. However, we found no statistical evidence that these morphological differences affected sprint speed. Colour morphs also exhibited different escape responses on the two substrates: in all species, dark morphs were less likely to immediately sprint from a simulated predator on white sand. As a result, escape response had a significant effect on sprint speed for two of the three species. Not surprisingly, all lizards sprinted faster on dark soil, which was probably due to the lizards' more immediate escape response and the higher compaction of dark soil. The relationship between escape response and sprint performance across the dark soil and white sand habitats suggests that behavioural differences may be an important component of adaptation and speciation in new environments. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 169–182.     

Influence of sprint speed and body size on predator avoidance in New Mexican spadefoot toads (<Emphasis Type="Italic">Spea multiplicata</Emphasis>)

Predator–prey interactions play an important role in community dynamics and may be important for promoting genetic diversification. Diversification may be especially important when prey species have multiple anti-predator strategies available, but these strategies conflict with each other. For example, rapid sprint speed and large size are both thought to decrease vulnerability to many predators. A physiological trade-off between swimming speed and growth rate has been documented in many aquatic species and, as a result, individual genotypes may employ one strategy or the other, but not both. Although rapid sprint speed is often assumed to decrease vulnerability to predators, this has only rarely been tested. Here I provide evidence that both rapid sprint speed and large size in tadpoles of the New Mexico spadefoot toad (Spea multiplicata) decreases predation risk from carnivore morphs of its congener the Great Plains spadefoot toad (Spea bombifrons). Such conflicts, coupled with spatio-temporal variation in predation pressure, may be important in maintaining genetic variation for trade-offs.     

Effects of Limb Length,Body Mass,Gender, Gravidity,and Elevation on Escape Speed in the Lizard Psammodromus algirus

Most animals rely on their escape speed to flee from predators. Here, we test several hypotheses on the evolution of escape speed in the lizard Psammodromus algirus. We test that: (1) Longer limbs should improve speed sprint. (2) Heavier lizards should be impaired regarding their sprint speed ability, suggesting a trade-off between fat storage and escape capability. (3) Males should achieve faster speeds due to their higher exposure to predators. (4) Gravid females, with increased body mass, should perform lower speed than non-gravid females. And (5) there are inter-population differences in sprint speed across an elevational gradient. We measured lizards sprint speed in a lineal raceway in the laboratory, filming races in standardized conditions and then calculating their maximal speed. We found that hind limb length greatly determined maximal sprint speed, lizards with longer limbs being faster. In parallel, higher body masses reduced maximal speed, which points to a trade-off between fat storage and escaping capability. Sexual differences also arose, as males were faster than females, as a consequence of males having longer limbs. Regarding females, gravidity did not impair maximal sprint speed, suggesting adaptations which compensate for the increased body mass. Finally, we found no elevational trend in both limbs length and sprint speed. In any case, this study suggests that selection on escape capacity may cast morphological evolution, and affect other life-history traits, such as fat storage and reproduction.     

The effect of 40-m repeated sprint training on maximum sprinting speed, repeated sprint speed endurance, vertical jump, and aerobic capacity in young elite male soccer players

The purpose of this study was to examine the effect of 10 weeks' 40-m repeated sprint training program that does not involve strength training on sprinting speed and repeated sprint speed on young elite soccer players. Twenty young well-trained elite male soccer players of age (±SD) 16.4 (±0.9) years, body mass 67.2 (±9.1) kg, and stature 176.3 (±7.4) cm volunteered to participate in this study. All participants were tested on 40-m running speed, 10 × 40-m repeated sprint speed, 20-m acceleration speed, 20-m top speed, countermovement jump (CMJ), and aerobic endurance (beep test). Participants were divided into training group (TG) (n = 10) and control group (CG) (n = 10). The study was conducted in the precompetition phase of the training program for the participants and ended 13 weeks before the start of the season; the duration of the precompetition period was 26 weeks. The TG followed a Periodized repeated sprint training program once a week. The training program consisted of running 40 m with different intensities and duration from week to week. Within-group results indicate that TG had a statistically marked improvement in their performance from pre to posttest in 40-m maximum sprint (-0.06 seconds), 10 × 40-m repeated sprint speed (-0.12 seconds), 20- to 40-m top speed (-0.05 seconds), and CMJ (2.7 cm). The CG showed only a statistically notable improvement from pre to posttest in 10 × 40-m repeated sprint speed (-0.06 seconds). Between-group differences showed a statistically marked improvement for the TG over the CG in 10 × 40-m repeated sprint speed (-0.07 seconds) and 20- to 40-m top speed (-0.05 seconds), but the effect of the improvement was moderate. The results further indicate that a weekly training with repeated sprint gave a moderate but not statistically marked improvement in 40-m sprinting, CMJ, and beep test. The results of this study indicate that the repeated sprint program had a positive effect on several of the parameters tested. However, because the sample size in this study is 20 participants, the results are valid only for those who took part in this study. Therefore, we advice to use repeated sprint training similar to the one in this study only in periods where the players have no speed training included in their program. Furthermore, the participants in this study should probably trained strength, however, benefits were observed even without strength training is most likely to be caused by the training specificity.     

Ontogenetic differences in the spatial ecology of immature Komodo dragons

The early life-history stages of reptiles are extremely important to an individual's fitness, but in an ecological sense, among the most difficult to observe. Here, we used radio-tracking techniques to describe the differences in movement patterns, habitat use and home range between hatchling and juvenile Komodo dragons Varanus komodoensis on Komodo Island, Indonesia. The movement of hatchlings from their nests was largely linear and suggested a natal dispersal event. The movement patterns of juvenile Komodo dragons exhibited a greater spatial overlap than hatchlings, indicating greater site fidelity and thus use of a more defined activity area. The rates of daily movement were significantly less for hatchlings compared with juvenile dragons. The activity areas of hatchlings were significantly smaller than juvenile dragons. Both age classes preferred utilizing dry monsoon forest compared with other habitat types. Hatchlings were predominantly arboreal compared with juveniles and the degree of arboreal activity was strongly correlated with an individual's size. These distinct differences in spatial ecology between immature life-history stages suggest that different selection pressures may affect different size classes of Komodo dragons.     

Sex-based differences and similarities in locomotor performance, thermal preferences, and escape behaviour in the lizard Platysaurus intermedius wilhelmi

Differences between sexes in physiological performance have received little attention in animals. We tested for sex differences in maximum sprint speed and maximal exertion over a range of temperatures in a population of Platysaurus intermedius wilhelmi lizards. We also examined sex-based differences in selected temperature range, mean field body temperatures (T(b)), and thermal activity limits. Finally, we conducted field studies to quantify male and female responses to a potential predator, which may be affected by their respective performance capabilities. Males were faster than females at all temperatures, and body size had no significant effect on sprint speeds. Males and females also selected similar T(b)'s when placed in a thermal gradient, but in the field, male lizards' T(b)'s were different from those of the females. However, predicted sprint speeds for males and females at their field T(b)'s are similar. No significant differences were found between males and females with regard to maximal exertion. When approached in the field, adult male lizards took refuge significantly earlier than did adult females and also fled over shorter distances, suggesting that females rely on crypsis as an escape strategy.     

Optimal body size with respect to maximal speed for the yellow-spotted monitor lizard (Varanus panoptes; Varanidae)

Studies of locomotor performance often link variation in morphology with ecology. While maximum sprint speed is a commonly used performance variable, the absolute limits for this performance trait are not completely understood. Absolute maximal speed has often been shown to increase linearly with body size, but several comparative studies covering a large range of body sizes suggest that maximal speed does not increase indefinitely with body mass but rather reaches an optimum after which speed declines. Because of the comparative nature of these studies, it is difficult to determine whether this decrease is due to biomechanical constraints on maximal speed or is a consequence of phylogenetic inertia or perhaps relaxed selection for lower maximal speed at large body size. To explore this issue, we have examined intraspecific variations in morphology, maximal sprint speed, and kinematics for the yellow-spotted monitor lizard Varanus panoptes, which varied in body mass from 0.09 to 5.75 kg. We show a curvilinear relationship between body size and absolute maximal sprint speed with an optimal body mass with respect to speed of 1.245 kg. This excludes the phylogenetic inertia hypothesis, because this effect should be absent intraspecifically, while supporting the biomechanical constraints hypothesis. The relaxed selection hypothesis cannot be excluded if there is a size-based behavioral shift intraspecifically, but the biomechanical constraints hypothesis is better supported from kinematic analyses. Kinematic measurements of hind limb movement suggest that the distance moved by the body during the stance phase may limit maximum speed. This limit is thought to be imposed by a decreased ability of the bones and muscles to support body mass for larger lizards.     

Effects of incubation temperature on growth and performance of the veiled chameleon (Chamaeleo calyptratus)

I evaluated the effect of incubation temperature on phenotypes of the veiled chameleon, Chamaeleo calyptratus. I chose this species for study because its large clutch size (30-40 eggs or more) allows replication within clutches both within and among experimental treatments. The major research objectives were (1) to assess the effect of constant low, moderate, and high temperatures on embryonic development, (2) to determine whether the best incubation temperature for embryonic development also produced the "best" hatchlings, and (3) to determine how a change in incubation temperature during mid-development would affect phenotype. To meet these objectives, I established five experimental temperature regimes and determined egg survival and incubation length and measured body size and shape, selected body temperatures, and locomotory performance of lizards at regular intervals from hatching to 90 d, or just before sexual maturity. Incubation temperature affected the length of incubation, egg survival, and body mass, but did not affect sprint speed or selected body temperature although selected body temperature affected growth in mass independently of treatment and clutch. Incubation at moderate temperatures provided the best conditions for both embryonic and post-hatching development. The highest incubation temperatures were disruptive to development; eggs had high mortality, developmental rate was low, and hatchlings grew slowly. Changes in temperature during incubation increased the among-clutch variance in incubation length relative to that of constant temperature treatments. J. Exp. Zool. 309A:435-446, 2008. (c) 2008 Wiley-Liss, Inc.     

孵化水热环境对渔异色蛇孵化卵和孵出幼体的影响

渔异色蛇卵孵化时能从环境中吸收水分导致质量增加,卵质量的增加与初始卵质量和孵化基质湿度有关。较大幅度的孵化基质湿度变化对孵化期、孵化成功率、胚胎动用孵内物质和能量、孵出幼体的性比、大小和质量无显著影响。孵化期随温度升高而缩短,并显示极强的窝间差异。温度对孵出幼体的性别无影响,但显著影响孵化成功率、胚胎对卵内物质和能量的动用、幼体的大小和质量、躯干和剩余卵黄的质量。孵出幼体总长的两性差异不显著,但雌体体长大于雄体而尾长小于雄体。３２℃不适于孵化渔异色蛇卵,该温度下孵出的幼体躯干发育不良,剩余孵黄较多,尾部均呈畸形,孵化过程中能量转化率较低。２４℃和２６℃中孵出的幼体躯干发育良好,孵化过程中能量转化率较高,各项被测定的幼体特征指标均极相似。     

Physiological control of water flux in conifers

Summary Pre-hatching developmental times for prosobranch gastropods are greatly influenced by temperature and taxonomic affinity. If the data used here (including all available data from the Muricacea) are a representative sample, then reasonably accurate estimates of developmental time can be obtained for most prosobranchs knowing only temperature and taxon. Times are also significantly affected by egg or hatching size. Correlations between developmental time and hatching form are probably accounted for by egg size. Prehatching periods are little, if at all, longer for metamorphosed hatchlings than for swimming hatchlings; in any event, differences are small relative to typical free swimming periods. Therefore, the planktonic period is a substantial addition to the total pre-juvenile period. Many embryos die before hatching. More would survive if development were faster; development is, therefore, prolonged at a measurable selective cost. Factors promoting extended developmental periods should be evaluated with these costs in mind. For example, providing much of the yolk as nurse-eggs may allow a species to have a large hatching size and at the same time a relatively brief developmental time.     

SPEED AND STAMINA TRADE-OFF IN LACERTID LIZARDS

Abstract.— Morphological and physiological considerations suggest that sprinting ability and endurance capacity put conflicting demands on the design of an animal's locomotor apparatus and therefore cannot be maximized simultaneously. To test this hypothesis, we correlated size‐corrected maximal sprint speed and stamina of 12 species of lacertid lizards. Phylogenetically independent contrasts of sprint speed and stamina showed a significant negative relationship, giving support to the idea of an evolutionary trade‐off between the two performance measures. To test the hypothesis that the trade‐off is mediated by a conflict in morphological requirements, we correlated both performance traits with snout‐vent length, size‐corrected estimates of body mass and limb length, and relative hindlimb length (the residuals of the relationship between hind‐ and forelimb length). Fast‐running species had hindlimbs that were long compared to their forelimbs. None of the other size or shape variables showed a significant relationship with speed or endurance. We conclude that the evolution of sprint capacity may be constrained by the need for endurance capacity and vice versa, but the design conflict underlying this trade‐off has yet to be identified.     

产卵于温暖且热稳定巢内的蜥蜴具有相对较高但较窄范围的孵化温度

作者用蜡皮蜥(Leiolepis reevesii)为模型动物,检验产卵于温暖且热稳定巢内的蜥蜴应有相对较高但较窄的孵化温度的假设。卵在三个恒定温度(27、30和33℃)、一个波动温度处理下孵化。温度的平均值而非方差影响孵化期,27、30和33℃的平均孵化期分别为101.1、69.6和55.3d。幼体性别不受孵化温度影响。不同处理孵出的幼体仅有稍许形态差异,但运动表现差异显著。27℃孵出幼体在跑道上的表现比其它处理孵出幼体差。卵能在27℃和33℃下孵化,但这两个孵化温度并不适宜。蜡皮蜥适宜的孵化温度范围可能处于最频繁的巢温变化范围(28℃-32℃)内。与其它在低温生境或温暖生境但产卵于浅巢的有鳞类爬行动物相比较,蜡皮蜥有相对较高但较窄适宜的卵孵化温度。因此,作者的数据支持上述假设。