宁波滑蜥两性异形和雌性繁殖

蜥蜴的雌性繁殖特征对理解两性异形的进化原因起着重要作用。于2011年4月在安徽滁州采集宁波滑蜥(Scincella modesta),定量研究该种形态特征的两性异形和雌性繁殖特征,检验成体形态特征两性异形与雌性繁殖的相关性。研究共采集43条(17♀♀,26♂♂)宁波滑蜥,雄性和雌性个体的最大体长分别为47.4 mm和46.6 mm。雌雄两性在体长和头宽上没有差异,而在腹长和头长上差异显著,雄性有较大的头长,雌性有较大的腹长。宁波滑蜥年产单窝卵。窝卵数和窝卵重与雌体体长及腹长呈正相关,卵重与雌体体长无相关性。窝卵数及卵重的变异系数分别为0.20和0.12。卵长径与窝卵数呈负相关,而卵短径与窝卵数无关。雌体主要通过增加窝卵数来增加繁殖输出。这些结果表明,宁波滑蜥是雌雄个体大小同形的两性异形模式,性选择使得雄性有着较大的头长,以具有较高的交配成功率,生育力选择使得雌性有着较大的腹长,以具有较大的生育力和繁殖输出。     

蜡皮蜥的两性异形和繁殖输出

为研究蜡皮蜥(Leiolepis reevesii)两性异形和繁殖输出,于2002、2003年4月下旬从海南乐东一种群捕获423头蜡皮蜥。经检测得到繁殖雌体的最小体长为89．0mm,据此判定≥89．0mm的个体为性成熟。研究结果表明：①蜡皮蜥具有两性异形,雄性大于雌性且具有较大的头部。成体雄性头长和头宽随体长的增长速率大于雌性,幼体头长和头宽随体长的增长速率无显著的两性差异。以性别和年龄(成、幼体)为因子的双因子ANOVA比较两性头长和头宽与体长的回归剩余值发现,雄性头部大于雌性,幼体头部相对大于成体。②饲养于实验室的母体中有42头于2002、2003年5月22日～7月16日产出正常卵,这些繁殖雌体具有年产多窝卵的潜力。窝卵数和卵重的变异系数分别为0．18和0．13,前者变异度大于后者。窝卵数、窝卵重和卵重均与母体体长无关。卵重与相对生育力之间无显著的负相关性,表明蜡皮蜥缺乏卵数量与卵大小之间的权衡。相对窝卵重与母体体长呈显著的负相关,表明较小的母体具有相对较大的繁殖输出。因雌体繁殖会滞缓其生长,小母体具有相对较大的繁殖输出,至少部分地解释了雌性蜡皮蜥的成体为什么个体较小。     

Variations in fecundity over catchment scales: Implications for caddisfly populations spanning a thermal gradient

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两种麻蜥卵和孵出幼体的特征

研究了山地麻蜥和丽斑麻蜥实验条件下的卵及孵出幼体的特征.山地麻蜥产卵雌体的体长大于丽斑麻蜥,窝卵重小于丽斑麻蜥,但平均卵重和相对窝卵重与丽斑麻蜥相似.两种蜥蜴均通过增加卵长径和卵短径来增加卵重,但卵的外形不同,山地麻蜥卵较长.两种蜥蜴卵孵化过程中均吸水增重.相似孵化条件(波动温度、-12 kPa)下,山地麻蜥的孵化期明显比丽斑麻蜥长.山地麻蜥幼体的尾、头部大于丽斑麻蜥,但体重和SVL相似.     

浙江丽水中国石龙子的食性、两性异形和雌性繁殖

丽水分布的中国石龙子（Ｅｕｍｅｃｅｓ ｃｈｉｎｅｎｓｉｓ）摄入的食物均为无脊椎动物,分别属于环节、软体和节肢动物,涉及３０余科,成体和幼体的食物生态位宽度分别为７．２６和６．６９,成体的幼体的食物生态们重叠度为０．５９。性成熟雄性个体大于雌体。成雄和幼体的头长和头宽随体长ＳＶＬ的增长速率大于成雌,成雄头长随ＳＶＬ的增长速度显著大于幼体,成雌和幼体的头长随ＳＶＬ的增长速率无显著差异。成雄头部大于成雌     

黑眶蟾蜍的两性异形与选型配对模式

本研究以黑眶蟾蜍(Duttaphrynus melanostictus)为研究对象,通过对比黑眶蟾蜍抱对个体的体长、头长、头宽、眼间距、鼓膜径、耳后腺长、眼径、前臂及手长、前肢长以及后肢长等形态特征,分析雌性黑眶蟾蜍繁殖输出与其体型的关系,探究黑眶蟾蜍两性异形模式及其与雌性生育力的关系;同时通过对配对个体形态学特征的相关性分析探究了黑眶蟾蜍的配对模式。结果表明,黑眶蟾蜍雌性体长和体重显著大于雄体;两性的所有局部形态特征均与体长成正相关;去除体长因素影响后,雄性头长以及后肢长均明显大于雌性,其余局部形态特征两性间则皆无显著差异。雌体的窝卵重、窝卵数均与其体长和体重成正相关关系。雌性成体的前肢长与抱对雄性成体的前肢长之间呈显著正相关,其余形态特征两性间均无相关性。研究表明,生育力选择是导致黑眶蟾蜍两性异形的重要驱动力;黑眶蟾蜍的选型配对模式未表现在个体大小上,而是体现在局部特征(前肢长),这不仅为揭示两栖类配对模式的普遍性提供了参考,还表明对两栖类选型配对的研究应以多个性状为对象。     

Life-history and ecological correlates of geographic variation in egg and clutch mass among passerine species

Broad geographic patterns in egg and clutch mass are poorly described, and potential causes of variation remain largely unexamined. We describe interspecific variation in avian egg and clutch mass within and among diverse geographic regions and explore hypotheses related to allometry, clutch size, nest predation, adult mortality, and parental care as correlates and possible explanations of variation. We studied 74 species of Passeriformes at four latitudes on three continents: the north temperate United States, tropical Venezuela, subtropical Argentina, and south temperate South Africa. Egg and clutch mass increased with adult body mass in all locations, but differed among locations for the same body mass, demonstrating that egg and clutch mass have evolved to some extent independent of body mass among regions. A major portion of egg mass variation was explained by an inverse relationship with clutch size within and among regions, as predicted by life-history theory. However, clutch size did not explain all geographic differences in egg mass; eggs were smallest in South Africa despite small clutch sizes. These small eggs might be explained by high nest predation rates in South Africa; life-history theory predicts reduced reproductive effort under high risk of offspring mortality. This prediction was supported for clutch mass, which was inversely related to nest predation but not for egg mass. Nevertheless, clutch mass variation was not fully explained by nest predation, possibly reflecting interacting effects of adult mortality. Tests of the possible effects of nest predation on egg mass were compromised by limited power and by counterposing direct and indirect effects. Finally, components of parental investment, defined as effort per offspring, might be expected to positively coevolve. Indeed, egg mass, but not clutch mass, was greater in species that shared incubation by males and females compared with species in which only females incubate eggs. However, egg and clutch mass were not related to effort of parental care as measured by incubation attentiveness. Ecological and life-history correlates of egg and clutch mass variation found here follow from theory, but possible evolutionary causes deserve further study.     

安徽滁州雌性丽斑麻蜥繁殖特征

在安徽滁州地区丽斑麻蜥(Eremias argus)年产两窝卵。窝卵数及窝卵重与雌体体长呈正相关,相对窝卵重与雌体体长无关,卵重与窝卵数无关。窝卵数、窝卵重及卵重在窝序间无明显的差异。卵长径与卵短径呈正相关,卵长径与窝卵数呈负相关,而卵短径与窝卵数无关。雌体主要通过增加窝卵数增加繁殖输出。     

Subsociality and female reproductive success in a mycophagous thrips: An observational and experimental analysis

Oviparous females of the haplodiploid, facultatively viviparous thrips Elaphrothrips tuberculatus(Thysanoptera: Phlaeothripidae) guard their eggs against female conspecifics and other egg predators. The intensity of maternal defense increases with clutch size. Field and laboratory observations indicate that cannibalism by females is an important selective pressure favoring maternal care. Experimental removals of guarding females showed that egg guarding substantially increases egg survivorship and that the survivorship of undefended eggs is higher in the absence of nonguarding female conspecifics than in their presence. The fecundity of viviparous females increases with the number of eggs cannibalized. The reproductive success of oviparous females increases with body size and local food density and decreases with local density of breeding females. Social behavior may not have advanced beyond maternal care in Elaphrothrips tuberculatusbecause, relative to Hymenoptera, capabilities for helping relatives are few or nonexistent, and the causes of variation in female reproductive success are not influenced easily by cooperation among females.     

中国石龙子雌体繁殖特征和卵孵化的地理变异

浙江丽水和广东韶关中国石龙子均年产单窝卵,窝卵数,窝卵重和卵重均与雌体SVL呈正相关,雌体头部形态,繁殖特征,产卵起始时间和孵孵化的热依赖性等有显著的地理变异;韶关石龙子产卵起始时间为5月中旬,比丽水经子约早两周,韶关石龙子窝卵数较大,卵较小,窝卵重与丽水石龙子无显著差异。韶关石龙子特定SVL的窝卵数比丽水石龙子多2．8枚卵,中国经子卵数量和大小之间有种群间权衡,无种数内权衡,同一种群内卵数量与卵大小无关,孵化温度影响石龙子孵出幼体的一些特征,24℃孵出细幼体比32℃孵出幼体大,躯干发育好,剩余卵黄少,韶关24℃孵出幼体的体重,躯干干重小于丽水幼体,韶关32℃孵出幼体的SVL小于丽水幼体,剩余卵黄大于丽水幼体,表明适宜卵孵化温度范围有地理变异。丽水石龙子卵对极端高温和低温的耐受性较强,适宜卵孵化温度范围较宽。     

Postural Shifts During Egg‐Brooding and Their Impact on Egg Water Balance in Children’s Pythons (Antaresia childreni)

Parental care typically consists of distinct behavioral components that are balanced to address the multiple needs of offspring. Female pythons exhibit post‐oviposition parental care in which they coil around their parchment‐shelled eggs throughout incubation (40–80 d). Subtle postural shifts during egg‐brooding facilitate embryonic gas exchange but may entail hydric costs to the clutch. This study used a simple behavioral model to (1) further quantify the costs and benefits of specific parental behaviors to developing offspring and (2) determine the influence that developmental stage and relative clutch mass have on parental behavior. Although previous research has demonstrated that egg‐brooding as a whole reduces clutch water loss, we hypothesized that egg‐brooding female pythons specifically adopt a tightly coiled posture to conserve embryonic water, but must make postural adjustments to enhance gas exchange between the clutch and nest environments at the cost of increased clutch water loss. We measured rates of water loss in brooding Children’s pythons (Antaresia childreni) and their respective clutches (i.e., brooding units) and monitored changes in brooding posture. We conducted serial trials to elucidate the effect of developmental stage on postural adjustments and water loss. Results demonstrated that the proportion of time females spent in a tightly coiled posture was inversely related to mean water loss from the brooding unit. Analyses indicated that slight adjustments in posture led to bursts in brooding unit water loss. Indeed, brooding unit water loss during postural adjustments was significantly higher than during tight coiling. These findings imply that python egg‐brooding provides an adjustable diffusive barrier that leads to discontinuous gas exchange, which minimizes clutch water loss. Because females with larger relative clutch masses spent more time tightly coiled, egg‐brooding female pythons may use a ‘water first’ strategy in which they intentionally conserve clutch water at the cost of reduced embryonic respiratory gas exchange.     

Parents benefit from eating offspring: density-dependent egg survivorship compensates for filial cannibalism

Abstract Why should animals knowingly consume their own young? It is difficult to imagine many circumstances in which eating one's own young (i.e., filial cannibalism) actually increases an individual's fitness; however, filial cannibalism commonly co‐occurs with parental care in fishes. The evolutionary significance of filial cannibalism remains unclear. The most commonly accepted explanation is that filial cannibalism is a mechanism by which caring males gain energy or nutrients that they reinvest into future reproduction, thereby increasing net reproductive success. There is mixed support for this hypothesis and, at best, it can only explain filial cannibalism in some species. A recent alternative hypothesis suggests that filial cannibalism improves the survivorship of remaining eggs by increasing oxygen availability, and thus increases current reproductive success. This theory has received little attention as of yet. We evaluated the hypothesis of oxygen‐mediated filial cannibalism in the sand goby by examining the effect of oxygen and egg density on the occurrence of filial cannibalism, evaluating the effects of partial clutch cannibalism on the survivorship of remaining eggs, and comparing potential costs and benefits of filial cannibalism related to the net number of eggs surviving. Indeed, we found that oxygen level and egg density affected the occurrence of cannibalism and that simulated partial clutch cannibalism improved survivorship of the remaining eggs. Additionally, because increased egg survivorship, stemming from partial egg removal, compensated for the cost of cannibalism (i.e., number of eggs removed) at a range of cannibalism levels, filial cannibalism potentially results in no net losses in reproductive success. However, oxygen did not affect egg survivorship. Thus, we suggest a more general hypothesis of filial cannibalism mediated by density‐dependent egg survivorship.     

Maternal investment in reproduction and its consequences in leatherback turtles

Maternal investment in reproduction by oviparous non-avian reptiles is usually limited to pre-ovipositional allocations to the number and size of eggs and clutches, thus making these species good subjects for testing hypotheses of reproductive optimality models. Because leatherback turtles (Dermochelys coriacea) stand out among oviparous amniotes by having the highest clutch frequency and producing the largest mass of eggs per reproductive season, we quantified maternal investment of 146 female leatherbacks over four nesting seasons (2001–2004) and found high inter- and intra-female variation in several reproductive characteristics. Estimated clutch frequency [coefficient of variation (CV) = 31%] and clutch size (CV = 26%) varied more among females than did egg mass (CV = 9%) and hatchling mass (CV = 7%). Moreover, clutch size had an approximately threefold higher effect on clutch mass than did egg mass. These results generally support predictions of reproductive optimality models in which species that lay several, large clutches per reproductive season should exhibit low variation in egg size and instead maximize egg number (clutch frequency and/or size). The number of hatchlings emerging per nest was positively correlated with clutch size, but fraction of eggs in a clutch yielding hatchlings (emergence success) was not correlated with clutch size and varied highly among females. In addition, seasonal fecundity and seasonal hatchling production increased with the frequency and the size of clutches (in order of effect size). Our results demonstrate that female leatherbacks exhibit high phenotypic variation in reproductive traits, possibly in response to environmental variability and/or resulting from genotypic variability within the population. Furthermore, high seasonal and lifetime fecundity of leatherbacks probably reflect compensation for high and unpredictable mortality during early life history stages in this species.     

Models of clutch size in insect oviposition

Models for clutch size in species where a female deposits eggs into a larval resource of limited carrying capacity are developed. Previous models of clutch size related mainly to vertebrates (notably birds) where parental care limits clutch size. Our models cover cases where a single female “saturates” a larval food patch with larvae. The main predictions are that (1) extra eggs should be laid to compensate for larval moratility; (2) clutches should generally be smaller than the size that yields the maximum number of surviving larvae/clutch; (3) in species that gain resources for eggs in the adult stage, clutch size will be unaffected by age-independent parental mortality between clutches; (4) clutch size should reduce throughout life in species that gain resources for eggs before the adult stage; (5) similar species, but which are constrained to produce constant-sized clutches, should lay smaller clutches if their total potential egg production is low; (6) clutch size should increase with increasing search costs for oviposition sites. An ESS model of double-oviposition (where two females sometimes lay in the same larval food patch) indicates that the first female should generally lay more eggs than the second female; the difference in clutch size should decrease as the probability of double-oviposition increases, and should decrease as the search costs for larval food plants decreases. Many of the predictions have some support from data on insect oviposition.     

Allometry of reproduction in two species of gekkonid lizards (Gehyra): effects of body size miniaturization on clutch and egg sizes

In squamate reptiles there is an allometric pattern for small-bodied females to have smaller clutches and proportionally larger eggs than large-bodied females, and this pattern occurs both among and within species. The allometric patterns in two species of the gecko Gehyra were studied to see how evolutionary reductions in adult body size affect fecundity and offspring size among species, and how these changes affect allometric relationships within species. Gehyra dubia has two eggs per clutch (the typical clutch size for gekkonid lizards), whereas the smallerbodied G. variegata has a single egg per clutch. Within both species, egg size increased with female body size. The data are consistent with at least two mechanistic hypotheses: (1) that the width of the pelvis constrains egg size; and (2) in species with invariant clutch sizes, larger females can only allocate additional energy towards egg size and not number. More direct tests of these hypotheses are warranted. Miniaturization of body sizes in Gehyra is correlated with a clutch size reduction of 50% (from two to one), and a large (1.7-fold) compensatory increase in relative egg mass. However, the small-bodied G. variegata (one egg per clutch) had a lower relative clutch mass than did G. dubia. These findings have implications for understanding the influence of evolutionary reductions in body size on reproductive traits, and for allometric trends in squamate reptiles in general.     

Variation of Reproductive Traits and Female Body Size in the Most Widely-Ranging Terrestrial Reptile: Testing the Effects of Reproductive Mode, Lineage, and Climate

The European common lizard, Zootoca vivipara, is the most widespread terrestrial reptile in the world. It occupies almost the entire Northern Eurasia and includes four viviparous and two oviparous lineages. We analysed how female snout-vent length (SVL), clutch size (CS), hatchling mass (HM), and relative clutch mass (RCM) is associated with the reproductive mode and climate throughout the species range and across the evolutionary lineages within Z. vivipara. The studied variables were scored for 1,280 females and over 3,000 hatchlings from 44 geographically distinct study samples. Across the species range, SVL of reproductive females tends to decrease in less continental climates, whereas CS corrected for female SVL and RCM tend to decrease in climates with cool summer. Both relationships are likely to indicate direct phenotypic responses to climate. For viviparous lineages, the pattern of co-variation between female SVL, CS and HM among populations is similar to that between individual females within populations. Consistent with the hypothesis that female reproductive output is constrained by her body volume, the oviparous clade with shortest retention of eggs in utero showed highest HM, the oviparous clade with longer egg retention showed lower HM, and clades with the longest egg retention (viviparous forms) had lowest HM. Viviparous populations exhibited distinctly lower HM than the other European lacertids of similar female SVL, many of them also displaying unusually high RCM. This pattern is consistent with Winkler and Wallin’s model predicting a negative evolutionary link between the total reproductive investment and allocation to individual offspring.     

Don'T put all your eggs in one nest: spread them and cut time at risk

Abstract In many egg-laying animals, some females spread their clutch among several nests. The fitness effects of this reproductive tactic are obscure. Using mathematical modeling and field observations, we analyze an unexplored benefit of egg spreading in brood parasitic and other breeding systems: reduced time at risk for offspring. If a clutch takes many days to lay until incubation and embryo development starts after the last egg, by spreading her eggs a parasitic female can reduce offspring time in the vulnerable nest at risk of predation or other destruction. The model suggests that she can achieve much of this benefit by spreading her eggs among a few nests, even if her total clutch is large. Field data from goldeneye ducks Bucephala clangula show that egg spreading enables a fecund female to lay a clutch that is much larger than average without increasing offspring time at risk in a nest. This advantage increases with female condition (fecundity) and can markedly raise female reproductive success. These results help explain the puzzle of nesting parasites in some precocial birds, which lay eggs in the nests of other females before laying eggs in their own nest. Risk reduction by egg spreading may also play a role in the evolution of other breeding systems and taxa-for instance, polyandry with male parental care in some birds and fishes.     

Clutch size limitation in waders: experimental test in redshank Tringa totanus

Several hypotheses have been raised to explain the upper limit of clutch size at four eggs in waders (suborder Charadrii), which may play an important role in the evolution of the variety of mating and parental care systems in this group. Experimental tests of the hypotheses have produced conflicting results. It was recently suggested that the combined effects of several incubation costs of a larger clutch suffice to limit its size to four eggs in this group. Here we test the incubation-limitation hypothesis in a field experiment, in redshank Tringa totanus. We created five-egg clutches by adding one egg from another nest to a just completed four-egg clutch. Four-egg control clutches were created by replacing one of the eggs by an egg from another nest. All egg removals, additions and replacements were done before incubation started. Incubation time in five-egg clutches increased by 1 day to 24.3ǂ.23 days, compared to 23.3ǂ.32 days in four-egg clutches. Egg hatchability and nest predation rates did not differ significantly between treatments. On average five-egg clutches produced one extra chick at hatching (4.5ǂ.26 chicks) compared to four-egg clutches (3.5ǂ.27 chicks). Also when several additional costs from incubating enlarged clutches are added, redshanks by laying a fifth egg would on average increase their reproductive success at hatching by an estimated 22%. The incubation-limitation hypothesis therefore is clearly rejected in this species. Possible mechanisms behind the four-egg clutch limit in waders and ways of testing the alternatives are discussed.     

A phylogenetic analysis of egg size,clutch size,spawning mode,adult body size,and latitude in reef fishes

Theoretical treatments of egg size in fishes suggest that constraints on reproductive output should create trade-offs between the size and number of eggs produced per spawn. For marine reef fishes, the observation of distinct reproductive care strategies (demersal guarding, egg scattering, and pelagic spawning) has additionally prompted speculation that these strategies reflect alternative fitness optima with selection on egg size differing by reproductive mode and perhaps latitude. Here, we aggregate data from 278 reef fish species and test whether clutch size, reproductive care, adult body size, and latitudinal bands (i.e., tropical, subtropical, and temperate) predict egg size, using a statistically unified framework that accounts for phylogenetic correlations among traits. We find no inverse relationship between species egg size and clutch size, but rather that egg size differs by reproductive mode (mean volume for demersal eggs = 1.22 mm³, scattered eggs = 0.18 mm³, pelagic eggs = 0.52 mm³) and that clutch size is strongly correlated with adult body size. Larger eggs were found in temperate species compared with tropical species in both demersal guarders and pelagic spawners, but this difference was not strong when accounting for phylogenetic correlations, suggesting that differences in species composition underlies regional differences in egg size. In summary, demersal guarders are generally small fishes with small clutch sizes that produce large eggs. Pelagic spawners and egg scatterers are variable in adult and clutch size. Although pelagic spawned eggs are variable in size, those of scatterers are consistently small.     

Production of insurance eggs in Nazca boobies: costs, benefits, and variable parental quality

Numerous studies of birds have demonstrated the value of producinginsurance eggs. We have previously found that second eggs provideinsurance against failure of first eggs for Nazca boobies (Sulagranti), which raise only one chick to fledging, yet some femaleslay only one egg. We used an 8-year data set to compare 2 hypothesesfor clutch size variation: one based on trade-offs, predictingdeclining future performance by females that lay a costly secondegg and one based on parental quality, predicting that intrinsicallysuperior females lay 2 eggs both currently and in the future.Clutch size variation did not contribute to the best multistatemark–recapture model of survival, suggesting that clutchsize and survival are unrelated and that any survival cost ofreproduction related to laying second eggs is small. Transitionprobabilities between reproductive states were generally, butnot entirely, inconsistent with fecundity costs of producinga marginal egg. Parental quality effects were apparent, withfemales tending to remain in a given reproductive state acrossseasons. Parents producing a marginal egg had consistently higherbreeding success than did parents of 1-egg clutches, due principallyto the insurance effect and secondarily to differences in parentalquality after hatching. Different model selection approachesgave differing results for logistic regression analyses of breedingsuccess of females that hatched eggs. A conventional significance-testing,iterative-fitting approach excluded insurance state from thetop model, whereas the information-theoretic (I-T) approachdetected an association between current insurance state andsubsequent survival and fecundity. Using the I-T approach, potentiallybiological significant (but not statistically significant underconventional analysis) effects were detected that may otherwisehave been ignored.