Reproductive strategies of female butterflies: variation in and constraints on fecundity

ABSTRACT.

• 1 This study first examines the reproductive strategy of female Speyeria mormonia Edwards (Lepidoptera: Nymphalidae):
• 2 Egg weight and number laid per day decrease with age.
• 3 Survival and daily egg number may be affected by temperature; mean daily egg weight is not affected by temperature.
• 4 Daily egg number is not correlated with body size. In the central range of body size, egg weight is also not correlated with body size. However, exceptionally large or small females lay respectively heavier or lighter eggs than average.
• 5 A simple trade-off between offspring size and number does not occur within females on a daily basis, or among females averaged over their lifespans.
• 6 Fat body resources are depleted at a rate independent of body size.
• 7 Females are essentially monogamous.
• 8 Age-specific fecundity data reported here for S.mormonia are next compared with data for other Lepidoptera with different adult feeding habits and egg maturation patterns, and hence different possibilities for adult feeding to play a role in egg production. Based on these comparisons, I propose that the shape of the age-specific fecundity curve for each species under optimal conditions is constrained by the potential importance of adult nutrients in egg production.

     

Size delays female senescence in a medium sized marsupial: The effects of maternal traits on annual fecundity in the northern brown bandicoot (Isoodon macrourus)

The degree to which females allocate resources between current reproduction, future fecundity and survival is a central theme in life history theory. We investigated two hypotheses proposed to explain patterns of reproductive investment, terminal investment and senescence, by examining the effects of maternal traits (age and maternal mass) on annual fecundity in female northern brown bandicoots, Isoodon macrourus (Marsupialia: Peramelidae). We found that annual fecundity in females declined in their final year of reproduction, indicating reproductive senescence. Maternal mass significantly influenced the rate of senescence and, in turn, a female's lifetime reproductive output. Mass had little effect on fecundity in 1st and 2nd year females, but a positive relationship with fecundity in 3rd year females. This meant that heavy, 3rd year females did not suffer the decline in fecundity shown in light 3rd year females. For 1st year females, mass and leg length increased between their first and second reproductive seasons, indicating a temporary shift, from the allocation of resources to reproduction, to increasing condition or structural size post their first breeding event. There were no net changes to body mass in subsequent years. We suggest that this year of post‐reproductive growth has important consequences for senescent effects on reproduction. Overall, results provided support for the effects of senescence on annual fecundity. Our findings were not consistent with the terminal investment hypothesis; reproductive output did not increase in females' final reproductive season despite a rapid decline in survival. However, this notion cannot be entirely dismissed; other measures of reproductive performance not examined here (e.g. offspring mass) may have provided an indication that females did increase their effort at the end of their lifespan. This study highlights the difficulty of measuring reproductive costs and the importance of understanding the combined effects of specific characteristics of an individual when interpreting reproductive strategies in iteroparous organisms.     

Influence of resource level on maternal investment in a leaf-cutter bee (Hymenoptera: Megachilidae)

Fisher's (1930) prediction of equal investment for each sexin a panmictic population is influenced by a number of ecologicalfactors, among which resource availability plays a major role,particularly when the population exists under changing resource availability.Rosenheim et al. proposed a multifaceted parental investment modelbased on the underlying assumption that individual females determine theirsex investment according to resource availability and oocyte availabilityto maximize reproductive success. The model predicts that greater availabilityof resources used for provisions will lead to (1) an increasein the proportion of females produced (when the female is thelarger sex) and (2) an increase in the amount of provisionsper offspring and thus an increase in offspring size. I testedthese predictions by a controlled experiment using a leaf-cutterbee, Megachile apicalis. I presented two levels of food resourcesto the nesting females, which were allowed to forage and nestin cages. The experimental results supported these parentalinvestment model's predictions.     

Condition and reproductive investment in the western mosquitofish (Gambusia affinis): little evidence for condition‐dependent sex‐biased investment

In sexually reproducing species, resources may theoretically be distributed with bias to the production of male or female offspring in response to the condition of the mother, commonly recognized as sex allocation. Using a recently characterized sex‐specific molecular marker, we tested for maternal sex allocation (i.e. maternal primary sex ratio bias and sex‐specific offspring investment) in captive laboratory‐bred western mosquitofish (Gambusia affinis) at early stages of offspring development. We found no statistical evidence to support sex allocation in G. affinis, based on maternal condition. In addition, we found little evidence for correlations between maternal condition and investment in the condition (mass) of individual offspring (of one sex or the other), although we did find that larger mothers tended to have higher fecundity.     

Dietary classification of extant kangaroos and their relatives (Marsupialia: Macropodoidea)

Kangaroos and kin (superfamily Macropodoidea) are the principal endemic herbivores of Australia and the most diverse radiation of marsupial herbivores ever to have evolved. As is typical of other herbivore groups (e.g. bovids), dietary niches span fruit, fungi, dicot leaves and monocot grasses in both specialists and generalists, but to date dietary classification has been largely ad hoc and poorly tied to actual dietary ecological data. Here we provide a simple dietary classification of the Macropodoidea based on an extensive literature survey. Intake of four major dietary items – grasses, dicot leaves, fruits and seeds, and fungi – was assessed using proportional intake for 19 species and categorical (ranked intake) data for 37 species. Statistical comparisons with cluster and principal components analyses aligned species into four dietary groups. Members of the first group have diets that primarily consist of fungi and fruits. Relative proportions of grasses to dicot leaves separate the remaining species into browser (more than 70% dicots), grazer (more than 70% grasses) and mixed feeder groups. Comparison of our diet‐based classification with a prevailing scheme based on dental morphology suggests that most species with what has traditionally been viewed as a ‘browser‐grade dentition’ are actually mixed feeders. This suggests that either morphology and diet are not tightly linked or that morphological differences between the dentitions of browsers and mixed feeders are subtle and have been overlooked. A positive correlation was found between body mass and average proportional intake of grass in the diet of macropodoids. This parallels the situation found in bovids, as well as the percentage cut‐off between dietary groups. These trends suggest that some underlying ecophysiological constraints may influence food choice in mammalian herbivores providing useful pointers to the diets of extinct taxa.     

Reproduction and sexual dimorphism in the viviparous lizard Sceloporus palaciosi (Squamata: Phrynosomatidae) from the Trans‐Mexican Volcanic Belt,Mexico

In this study, sexual dimorphism, reproductive cycles, litter size and offspring size of a population of the little‐known species Sceloporus palaciosi in central Mexico were analysed. Significant male‐biased sexual size dimorphism was recorded in snout–vent length (SVL), head length, head width, forearm length and tibia length. Both sexes showed asynchronous reproductive cycles, and males reached sexual maturity at a smaller SVL (33 mm) than females (37 mm). Testes volumes were small from January to February, testicular recrudescence began from March to June, and decreased in July, but increased again in August and September, followed by a second decrease from October to December. In females, vitellogenesis began from May until ovulation in December. Embryonic development extended from November to March, and a small number of females carried embryos through July. Mean litter size was 4.0 and was positively correlated with female SVL. The length of the reproductive period in S. palaciosi recorded in this study is longer than that recorded for other populations in other parts of this species range. Further studies are needed to clarify reproductive cycles in the other isolated populations of S. palaciosi, and then extended to other species and chromosome races in the Sceloporus grammicus complex.     

Fitness consequences of floral variation in Senecio jacobaea (Asteraceae): evidence from a segregating hybrid population and a resource manipulation experiment

The present study examines some of the ecological factors that might exert selection on floral morphology in Senecio jacobaea , a self-sterile composite which exhibits geographic variation in the frequency of rayed and discoid individuals. Regression analyses of phenotypic data from a large, segregating hybrid population, established in a semi-natural (garden) environment and studied over a 2-year period, revealed a negative relationship between the size of the rays and the average germination rate of the maternal seed crop, a pattern that can be attributed to the reduced germination speed of achenes from ray florets. There was no effect of ray size on the amount of cross-pollination achieved, the proportion of heads infested by larvae of seed flies ( Pegohylemyia ) and the amount of resources retained for the next flowering season. The lack of resource costs was also apparent in a manipulation experiment with greenhouse-grown plants of the rayed phenotype: artificial removal of all rays at the early bud or flowering stage had no detectable effect on subsequent flower and fruit development, regardless of whether the plants experienced high or low water stress. Given these and other observations, I hypothesize that plant-animal interactions and resource costs sometimes play a minor role in exerting selection on flower morphology and that spatially varying selection on germination behaviour accounts for some of the morph frequency variation in S. jacobaea.     

Coexistence of perlid stoneflies (plecoptera): Predictions from multivariate morphometrics

Ecological compatibility of the nymphs of 5 stonefly genera (Plecoptera : Perlidae) was predicted from a principal components ordination of metric data on 22 trophic and locomotor structures. Nymphs of these taxa follow different allometry relationships and are more similar at some sizes than others. Coexistence probabilities (0, .5, 1.0) were estimated from proximity in morphological space, assumed independent, and multiplied to obtain assemblage probabilities of multispecies sets. Combinations with P_c = 1 occur in western U.S.A. but only 1 of 20 sets with Pc 0.5 is known to exist.     

寄主植物对水椰八角铁甲发育历期、取食和繁殖的影响

本文探讨了加拿利海枣Phoenix canariensis、 棕榈Trachycarpus fortunei、 刺葵Phoenix hanceana和蒲葵Livistona chinensis）4种寄主植物对水椰八角铁甲Octodonta nipae (Maulik)取食和产卵的影响, 并分析了寄主植物叶片中影响该虫取食量、 产卵量的主要营养成分。结果表明： 水椰八角铁甲对上述4种寄主的选择有显著差异, 偏好加拿利海枣和棕榈, 而对蒲葵的选择性最差。4种寄主植物叶片中主要营养成分含量差异显著（粗脂肪： F_3,8=153.508, P=0.000; 可溶性糖： F_3,8=56.922,P=0.000; 可溶性蛋白： F_3,8=150.309, P=0.000; 游离氨基酸： F_3,8=41.278, P=0.000）, 其中加拿利海枣中可溶性糖、 可溶性蛋白和游离氨基酸含量均较高, 分别为1.13%, 1.05%和19.50%; 蒲葵中粗脂肪含量较高, 为7.04%, 其余3种营养成分含量均较低。主成分分析表明游离氨基酸、 可溶性糖和可溶性蛋白是影响水椰八角铁甲取食、 产卵的主要因素, 与取食量和产卵量均显著相关, 贡献率分别为56.1%, 26.7%和13.7%。该研究对于分析水椰八角铁甲的寄主适应性变异及其机理等均具有重要意义。     

Optimal progeny body size in a solitary bee,Osmia bicornis (Apoidea: Megachilidae)

1. Females of solitary, nest‐constructing bees determine both sex (haplo‐diploidy) as well as body size (by amount of provision) of each single offspring. 2. According to the Optimal Allocation Theory, females should allocate resources in portions that maximise fitness returns. A key fitness component in bees is body size that is determined solely by the provisions supplied by the mother. 3. The optimal progeny body size relies on different factors in both sexes. In females, provision efficiency is crucial for reproductive success. In males, however, fitness depends primarily on mating success. 4. Provision efficiency of Osmia bicornis L. females depends on the capacity to stow pollen (scopa) and their ability to carry the packed loads. Scopa capacity increases isometrically with body size whereas indices of flight performance (EPI, free lift) decrease. These complementary effects substantially contribute to the adjustment of optimal body size in daughters. 5. The impact of body mass on fitness of males is determined by the mating system. Owing to the opportunistic polygyny in O. bicornis, there was no detectable correlation between body size and male mating success. Consequently, mother bees distribute their provisions to many, but small sons to increase the number of descendant competitors in the race for matings. Optimal body size in sons is a trade‐off between a large male advantage in rare scrambles over receptive females and small‐size‐related disadvantages in viability.     

Sexual maturity and estimated fecundity in female Indo‐Pacific bottlenose dolphins (Tursiops aduncus) from South Australia: Combining field observations and postmortem results

Knowledge of life history of bottlenose dolphins in Australia is limited, with no studies comparing field and postmortem data from the same region. Carcasses of 88 opportunistically collected females (1987–2015) were studied, including eight observed for up to 23 yr before death. Ovaries were weighed and number of corpora determined grossly. Nineteen mammary glands were examined histologically. Relative age was determined using developmental features and body length, estimated age by tooth incremental lines, and physical maturity by epiphyseal fusion. Age at sexual maturation was 7.17 yr (6–>14 yr) at body lengths of 191–209 cm. Physical maturation occurred at 12–17 yr, and body lengths of 195–233 cm. An Exponential model provided the best fit for age at body length, with an asymptote at 214 cm. Combined ovary weight increased between birth and sexual maturation, with significantly more corpora in the left ovary. Corpora increased with age and appeared to persist throughout life. For mature females, 95% had ≤ 11 corpora. Number of corpora was consistent with number of calves for females with known life histories. Estimated interbirth period was about 4 yr. Three females with abnormal reproductive features were either chronically diseased and/or had high heavy metal burdens.