A comparative study of egg mass and clutch size in the Anseriformes

The factors explaining interspecific differences in clutch investment in precocial birds are poorly understood. We investigated how variations in clutch characteristics are related to environmental factors in a comparative study of 151 extant species of ducks, geese and swans (Anseriformes). Egg mass was negatively related to clutch size in a phylogenetic regression, a relationship that was much stronger when controlling for female mass. Nest placement was related to both egg size and clutch size, with cavity-nesting species laying more but smaller eggs. Egg size was positively correlated with incubation period and with female mass, and also with sexual size dimorphism (i.e. male mass relative to that of the female). Clutch size was not related to female mass. Species with long term pair bonds laid smaller clutches and larger eggs. The size of the breeding range was strongly positively correlated with clutch size and clutch mass, and its inclusion in multivariate models made other biogeographical variables (hemisphere, breeding latitude or insularity) non-significant. The small clutches in insular species appear to be a product of small range size rather than insularity per se. Our results suggest there is an evolutionary trade-off between clutch and egg size, and lend support to Lack’s resource-limitation hypothesis for the waterfowl.     

A large‐scale latitudinal pattern of life‐history traits in a strictly univoltine damselfly

1. Variation in thermal conditions and season length along latitudinal gradients affect body size‐related traits over different life stages. Selection is expected to optimise these size traits in response to the costs and benefits. 2. Egg, hatchling, larval and adult size in males and females were estimated along a latitudinal gradient of 2730 km across Europe in the univoltine damselfly Lestes sponsa, using a combination of field‐collection and laboratory‐rearing experiments. In the laboratory, individuals were grown in temperatures and photoperiod simulating those at the latitude of origin, and in common‐garden conditions. 3. The size of adults sampled in nature was negatively correlated with latitude. In all populations the females were larger than the males. Results from simulated and common‐garden rearing experiments supported this pattern of size difference across latitudes and between sexes, suggesting a genetic component for the latitudinal size trend and female‐biased size dimorphism. In contrast, hatchling size showed a positive relationship with latitude, but egg size, although differing between latitudes, showed no such relationship. 4. The results support a converse Bergmann cline, i.e. a negative body size cline towards the north. This negative cline in body size is probably driven by progressively stronger seasonal time and temperature constraints towards the higher latitudes and by the obligate univoltine life cycle of L. sponsa. As egg size showed no relationship with latitude, other environmental factors besides temperature, such as desiccation risk, probably affect this trait.     

Geographical variation in egg size of the Great Tit Parus major: a new perspective

A recent study on geographical variation in egg size of Great Tits Parus major concluded that: (1) mean egg size tended to increase with increasing latitude; and (2) mean egg size was positively correlated with mean clutch size. Including new data on both egg and clutch size, we reanalysed the relationships between egg size, clutch size and latitude, and investigated the possible effects of habitat type, female body size and egg shape on these relationships. We found that (1) egg volume showed minimum values around 51°N, increasing both north and southwards; (2) female body size increased linearly with increasing latitude; (3) female body size was positively correlated with egg breadth, but not with egg length or egg volume; (4) the sphericity index of the eggs (breadth to length ratio) was largest at medium latitudes, and eggs were more elongated towards the north and the south; (5) the relationship between clutch size and latitude was curvilinear, with the largest clutch sizes at intermediate latitudes; (6) egg size was not correlated with clutch size when the complete latitudinal range was considered, but egg size was negatively correlated with clutch size between 40 and 51°N; and (7) egg size did not differ among habitat types. We suggest that female body size (which probably limits egg breadth), and the pressure for producing large eggs (which in turn increases the reproductive success) are the main determinants of geographical variation in egg size and shape. Populations of small-bodied Great Tits seem to escape from the limits of their size, producing relatively elongated eggs, so that from a certain latitude southwards, egg volume does not decrease in spite of a decrease in female body size. Moreover, the negative relationship between egg and clutch size at low latitudes suggests that energetic trade-offs may also contribute to determine egg size in the south.     

Sexual dimorphism in leg length among orb-weaving spiders: a possible role for sexual cannibalism

The degree and direction of sexual dimorphism across different species is commonly attributed to differences in the selection pressures acting on males and females. The extent of these differences is especially apparent in species that practise sexual cannibalism, where the female attempts to capture and eat a courting male. Here, we investigate the relationship between sexual dimorphism in size and leg length, sexual cannibalism and courtship behaviour in three taxonomic groups of orb-weaving spiders, using morphological data from 249 species in 36 genera. Females are larger than males in all three taxonomic groups, and males have relatively longer legs than females in both the Araneinae and Tetragnathidae. Across genera within each taxonomic group, male body size is positively correlated with both female body size and male leg length, and female body size is positively correlated with female leg length. Sexual size dimorphism is negatively correlated with relative male leg length within the Araneinae, but not within either the Tetragnathidae or the Gasteracanthinae. There was no negative correlation between sexual size dimorphism and relative female leg length in any taxonomic group. We argue that the relationship between sexual size dimorphism and relative male leg length within the Araneinae may be the result of selection imposed by sexual cannibalism by females.     

Ecological correlates of body size and egg size in parasitic Ascothoracida and Rhizocephala (Crustacea)

In order to identify key factors in the evolution of life history traits in Ascothoracida and Rhizocephala (two groups of crustacean parastes of invertebrates), comparative analyses were performed using phylogenetically independent contrasts. Among 59 ascothoracidan species, latitude correlated positively with body size, whereas there was no relationship between water depth and body size. Body size also correlated strongly with egg size; however, once corrected for body size, egg size was not related to either latitude or water depth. Among 91 rhizocephalan species, neither latitude nor water depth correlated with body size. However, host species of larger sizes harboured larger species of rhizocephalan parasites. Egg size of rhizocephalans did not correlate with body size, and was not influenced by either latitude or water depth. The patterns observed in this study show both differences from an similarities to those reported for other groups of crustacean parasites, and suggest that adaptations to similar selective pressures are not always identical among distantly-related taxa.     

Uncertain branch lengths, taxonomic sampling error, and the egg to body size allometry in temperate butterflies (Lepidoptera)

The allometry of egg to body size in temperate butterflies, and the relationships between egg size and larval host structure, taxonomy, voltinism, and duration of the egg stage, are investigated using cross-species analysis and the comparative analysis of independent contrasts. In addition, the effect of two sources of uncertainty that may affect continuous data when treated under a statistical, comparative, framework, is assessed: (1) unknown evolutionary distances, and (2) taxonomic representativity (proportion of species of a given taxon, from which data are available). It is suggested that the effects of taxonomic under-representation could be important in comparative, quantitative studies, but this problem may be tempered by means of weighted regression. Under the assumption that taxonomy represents butterfly phylogeny, egg and adult body size are related by negative allometry (i.e. the slope of the line fitted to the logarithmically transformed data is lower than 1.0). However, the precise slope (0.2-0.9) depends on the method used, branch lengths, and taxonomic sampling. There is evidence for a relationship between a species' voltinism and the number of days it spends in the egg stage, as well as between adult butterfly size and the gross structure of the plants used as larval hosts (woody plants or herbs). Egg size proves to be related to foodplant taxonomy, voltinism, and duration of the egg stage when the data are analysed using species means, but these relationships become non-significant when the comparative method is employed.     

Limited male incubation ability and the evolution of egg size in shorebirds

In bird species where males incubate but are smaller than females, egg size may be constrained by male body size, and hence ability to incubate the eggs. Using data from 71 such shorebird species, we show that egg size decreases as the degree of female-biased sexual size dimorphism increases, after controlling for female body mass. Relative egg size was not related to mean clutch size. However, when controlling for mating system, the relationship between female-biased sexual size dimorphism and relative egg size was only significant in polyandrous species. The relatively small eggs of socially polyandrous shorebirds have previously been explained as an energy-saving strategy associated with the production of multiple clutches. Our findings suggest that egg size evolution is better explained by male incubation limitation in these birds.     

Spatial and environmental effects on Coho Salmon life history trait variation

Adult size, egg size, fecundity, and mass of gonads are affected by trade‐offs between reproductive investment and environmental conditions shaping the evolution of life history traits among populations for widely distributed species. Coho salmon Oncorhynchus kisutch have a large geographic distribution, and different environmental conditions are experienced by populations throughout their range. We examined the effect of environmental variables on female size, egg size, fecundity, and reproductive investment of populations of Coho Salmon from across British Columbia using an information theoretic approach. Female size increased with latitude and decreased with migration distance from the ocean to spawning locations. Egg size was lowest for intermediate intragravel temperature during incubation, decreased with migration distance, but increased in rivers below lakes. Fecundity increased with latitude, warmer temperature during the spawning period, and river size, but decreased in rivers below lakes compared with rivers with tributary sources. Relative gonad size increased with latitude and decreased with migration distance. Latitude of spawning grounds, migratory distance, and temperatures experienced by a population, but also hydrologic features—river size and headwater source—are influential in shaping patterns of reproductive investment, particularly egg size. Although, relative gonad size varied with latitude and migration distance, how gonadal mass was partitioned gives insight into the trade‐off between egg size and fecundity. The lack of an effect of latitude on egg size suggests that local optima for egg size related to intragravel temperature may drive the variation in fecundity observed among years.     

Fecundity, lifespan and egg mass in butterflies: effects of male-derived nutrients and female size

1. Effects of larval reserves and nutrients received as adults on fecundity and lifespan in female Danaus plexippus (the Monarch Butterfly) were measured to determine the relative importance of different sources of nutrients for reproduction and somatic maintenance.
2. Egg-laying lifespan was correlated with female size but not with the amount of male-derived nutrients or adult food concentration.
3. Lifetime fecundity was higher when females received a large first spermatophore, but was not affected by female size when lifespan was controlled or by adult food concentration.
4. At the end of their lives, females contained unlaid eggs and retained, on average, 88% of their initial mass. This proportion was unchanged in two years, although mean egg-laying lifespan varied from 22·5 to 28·7 days.
5. Egg mass decreased over the female lifespan, and was correlated with female size.
6. These results suggest that larval reserves are more important for somatic maintenance than adult income, but that the protein-rich nutrients received from males contribute to egg production. This supports theoretical predictions and empirical studies of other Lepidoptera showing that larval reserves are less likely to affect fecundity when the adult income can contribute substantially to egg production.     

Sexual size dimorphism and reproductive ecology in relation to mating system in waders

The relationship between sexual size dimorphism, body-weight and different reproductive traits (e.g. clutch size, egg weight and incubation period) in relation to mating system and forms of parental care was studied in waders. Two hypotheses were examined. (1) Sexual size dimorphism is correlated with the intensity of sexual selection. (2) The degree of sexual size dimorphism is the result of an interrelationship between the reproductive strategy of the female and her body size. In the polygynous species the male was significantly larger than the female. This is consistent with the sexual selection hypothesis. However, among waders, a positive correlation exists between egg weight, clutch mass and body-weight. Selection for small eggs or a short incubation period may therefore have an influence on female body-weight. If the lack of paternal care reduces the female's possibility for producing large eggs or incubating a large clutch mass, we would expect a selection pressure for small female size among polygynous species. Thus, large sexual size dimorphism among polygynous waders may be a result of selection for small female size to lack of paternal care, or selection for large male size due to intramale competition or a female preference for large-sized males. In multiple-clutch species (viz. species in which the female regularly lays more than one clutch during the season) egg weight was low both for a given female and male body-weight. The low egg weight of multiple-clutch species is assumed to be a result of the constraints placed on the female from producing several clutches during a single breeding season.     

A Test of Rensch’s Rule in Greater Horseshoe Bat (Rhinolophus ferrumequinum) with Female-Biased Sexual Size Dimorphism

Sexual size dimorphism (SSD) is widespread within the animal kingdom. Rensch’s rule describes a relationship between SSD and body size: SSD increases with body size when males are the larger sex, and decreases with body size when females are the larger sex. Rensch’s rule is well supported for taxa that exhibit male-biased SSD but patterns of allometry among taxa with female-biased size dimorphism are mixed, there is evidence both for and against the rule. Furthermore, most studies have investigated Rensch’s rule across a variety of taxa; but among-population studies supporting Rensch’s rule are lacking, especially in taxa that display only slight SSD. Here, we tested whether patterns of intraspecific variation in SSD in greater horseshoe bats conform to Rensch’s rule, and evaluated the contribution of latitude to Rensch’s rule. Our results showed SSD was consistently female-biased in greater horseshoe bats, although female body size was only slightly larger than male body size. The slope of major axis regression of log₁₀ (male) on log₁₀ (female) was significantly different from 1. Forearm length for both sexes of greater horseshoe bats was significantly negatively correlated with latitude, and males displayed a slightly but nonsignificant steeper latitudinal cline in body size than females. We suggest that variation in patterns of SSD among greater horseshoe bat populations is consistent with Rensch’s rule indicating that males were the more variable sex. Males did not have a steeper body size–latitude relationship than females suggesting that sex-specific latitudinal variation in body size may not be an important contributing factor to Rensch’s rule. Future research on greater horseshoe bats might best focus on more comprehensive mechanisms driving the pattern of female-biased SSD variation.     

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。     

SEXUAL SIZE DIMORPHISM AND EGG-SIZE ALLOMETRY IN BIRDS

We tested the hypothesis that egg size should evolve in sexually dimorphic birds to reduce costs associated with more rapid growth by nestlings of the larger sex. Consistent with this hypothesis, we found that in species in which males were larger, females laid proportionately larger eggs as sexual size dimorphism increased. However, this result was also consistent with the hypothesis that egg size varied allometrically with both male and female body size. Furthermore we found that in species in which females were larger, relative egg size decreased as size dimorphism increased, which is consistent with the “allometry hypothesis” but not the “cost-reduction hypothesis. That male body size contributes to the allometric relationship between egg size and body size suggests that the basis for the allometric relationship is not wholly a mechanical one stemming from the physical requirements of developing, transporting, and laying an egg of a particular size. Rather, the relationship seems likely to be tied more directly to body size itself the tact that male body size influences a female trait suggests that egg size–body size relationships otter some scope for investigating the basis for allometric relationships in general.     

Fitness consequences of egg-size variation in the lesser snow goose

We investigated the relationship between eggsize variation and (a) egg hatching success, (b) chick survival to fledging and recruitment, and (c) adult female survival, over 12 years in the lesser snow goose (Anser caerulescens caerulescens). By comparing the means and variances of egg size for successful and unsuccessful eggs, our aim was to assess the relative fitness of eggs of different sizes and to determine the type of selection operating on egg size in this species. As both egg size and reproductive success vary with age in the lesser snow goose we controlled for the effects of female age. Egg-size variation is very marked in this population, varying by up to 52% for eggs hatching successfully. However, there was no relationship between egg size and post-hatching survival of goslings to fledging or recruitment, either within or between broods, pooling across years. Egg size varied significantly between successful and unsuccessful clutches in only 2 of 33 individual year comparisons. First-laid eggs surviving to onset of incubation, and eggs hatching successfully, were on average larger than unsuccessful eggs, but this was probably due to the confounding effects of female age-specific and sequence-specific egg survival. Variance of egg size differed significantly between successful and unsuccessful eggs in only 3 of 24, and 0 of 21, individual year comparisons for pre- and post-hatching survival respectively. We therefore found little evidence for a relationship between egg-size variation and offspring fitness, or for strong directional, normalising or diversifying selection operating on egg size, in the lesser snow goose. In addition, there was only weak support for the hypothesis that egg-size variation is maintained by temporal variation in selection pressure (sensu Ankney and Bisset 1973). It is likely that egg-size variation represents the pleiotropic expression of alleles affecting more general physiological or metabolic processes. While this does not rule out the existence of alleles with more direct effects on egg size we suggest that their contribution to heritable egg size is small.     

Female‐biased dimorphism in size and age at maturity is reduced at higher latitudes in lake whitefish Coregonus clupeaformis

Female‐biased sexual dimorphism in size at maturity is a common pattern observed in freshwater fishes with indeterminate growth, yet can vary in magnitude among populations for reasons that are not well understood. According to sex‐specific optimization models, female‐biased sexual size dimorphism can evolve due to sexual selection favouring earlier maturation by males, even when sexes are otherwise similar in their growth and mortality regimes. The magnitude of sexual size dimorphism is expected to depend on mortality rate. When mortality rates are low, both males and females are expected to mature at older ages and larger sizes, with size determined by the von Bertalanffy growth equation. The difference between size at maturity in males and females becomes reduced when maturing at older ages, closer to asymptotic size. This phenomenon is called von Bertalanffy buffering. The predicted relationship between the magnitude of female‐biased sexual dimorphism in age and size at maturity and mortality rate was tested in a comparative analysis of lake whitefish Coregonus clupeaformis from 26 populations across a broad latitudinal range in North America. Most C. clupeaformis populations displayed female‐biased sexual dimorphism in size and age at 50% maturity. As predicted, female‐biased sexual size dimorphism was less extreme among lower mortality, high‐latitude populations.     

Developmental rate estimation and life table analysis for Halyomorpha halys (Hemiptera: Pentatomidae)

Egg and nymphal development were studied under constant temperatures for the newly introduced pest species, Halyomorpha halys (St?l) (Hemiptera: Pentatomidae). Development was assessed at seven constant temperatures (15-35 degrees C). Development to adult was completed at temperatures between 17 and 33 degrees C, with egg hatch also occurring at 15 degrees C. The relationship between temperature and developmental rate was evaluated using three developmental models. Of the models evaluated, the Briere-1 model was the best fit for the empirical data of egg and total development and for providing accurate values for the temperature threshold. Application of the linear degree-day model estimated 537.63 DD are needed for total development (egg to imaginal ecdysis). An additional 147.65 DD are needed for the preoviposition period of the female. Reproductive parameters were evaluated at 25 degrees C and indicate a median number of 28 eggs per egg mass. Oviposition occurred at 4.32-d intervals, and a female can continue to oviposit throughout its lifespan. H. halys is univoltine in New Jersey and Pennsylvania, but if it spreads to warmer climates in the United States, it could have multiple generations per year.     

Variations in clutch and egg sizes in the amphidromous goby <Emphasis Type="Italic">Rhinogobius</Emphasis> sp. CB along a river course and within a spawning season

Rhinogobius sp. CB is a common amphidromous goby in Japan. I investigated egg and clutch sizes along a river course and within a spawning season in the Aizu River, Kii Peninsula, Japan. Clutch size within the same female size did not differ along the course of the river, but decreased from early to later in the spawning season. Egg size within the same female size decreased from early to later in the spawning season and from the upper to the lower reaches. These results mean energy resources allocated to the ovary decreased seasonally and locally. Several factors are presented to explain these variations, such as female somatic conditions, a tradeoff between reproduction and growth, food availability, water temperature, and presence of competitive species. Some factors explaining the seasonal and local variations in egg size, such as water temperature and food availability for offspring, are also presented. Egg size correlated well with female size. The trend in egg size variation with female size seems to be an adaptation for their migrating pattern, as larvae from larger female, which tended to inhabit the upper reaches, would have a greater endurance against starvation during their migration to the sea.     

Egg size decreases with increasing female tail fork depth in family Hirundinidae

Female ornamentation evolves as a nonfunctional copy of functional male ornamentation or through direct selection on female ornamentation. Because females invest many resources in both reproduction and ornamentation, an evolutionary tradeoff between female ornamentation and maternal investment can be predicted, but it has rarely been demonstrated. Using phylogenetic comparative analysis, we studied egg size in relation to female fork depth in the family Hirundinidae, which has a wide range of fork depth (from 0 to >50 mm). Because deeply forked tails are aerodynamically costly, we predicted that species in which females have deeply forked tails suffer reduced egg size due to inefficient foraging during the egg formation period. Egg length was significantly related to nest type but not to female or male tail fork depth, whereas we found a significant negative relationship between egg breadth and female, but not male, tail fork depth. As a consequence, a significant negative relationship was found between egg volume and female, but not male, tail fork depth. Because female and male fork depths were not significantly related to clutch size, clutch size would not compensate the relationship between egg size and fork depth. The current finding supports the hypothesis that female ornamentation trades off with maternal investment.     

高温对稻褐飞虱发育与生殖的影响

通过高温处理及交配产卵实验,探讨了高温对稻褐飞虱Nilaparvata lugens (Stal)发育与生殖的影响。研究了不同高温条件对褐飞虱若虫发育历期、产卵量、产卵前期、寿命等生物学特性的影响。34℃以上高温导致褐飞虱若虫发育历期延长。高温处理4龄若虫使羽化后的雌成虫产卵量减少。高温处理不同日龄雌成虫也致使其产卵量减少,其中以1日龄短翅型、3日龄长翅型的产卵量影响最大。高温处理后褐飞虱寿命缩短。高温恒温处理,对短翅型雌成虫的产卵前期影响不大,但能延长长翅型雌成虫的产卵前期;而高温变温处理致使短、长翅型雌成虫的产卵前期均延长。高温变温对褐飞虱生殖的影响程度大于高温恒温。高温处理组雌、雄成虫与对照组相应的成虫交配试验表明,高温对雌性的影响大于雄性。实验初步确定34℃为对褐飞虱发育与生殖产生影响的临界温度。     

海南睑虎繁殖生物学特征初步观察

关于睑虎属(Goniurosaurus)物种的研究主要集中在新种描述、分类分布以及系统进化等方面,繁殖生物学资料基本空白.本课题组于2017年9月至2019年8月对海南吊罗山国家级自然保护区内海南睑虎(G.hainanensis)的繁殖生物学特征进行了调查研究.结果发现,海南睑虎的繁殖期为3～10月,共观察到雌性个体1...