Measuring temporal variation in reproductive output reveals optimal resource allocation to reproduction in the northern grass lizard, Takydromus septentrionalis

We measured the reproductive output of Takydromus septentrionalis collected over 5 years between 1997 and 2005 to test the hypothesis that reproductive females should allocate an optimal fraction of accessible resources in a particular clutch and to individual eggs. Females laid 1–7 clutches per breeding season, with large females producing more, as well as larger clutches, than did small females. Clutch size, clutch mass, annual fecundity, and annual reproductive output were all positively related to female size (snout–vent length). Females switched from producing more, but smaller eggs in the first clutch to fewer, but larger eggs in the subsequent clutches. The mass-specific clutch mass was greater in the first clutch than in the subsequent clutches, but it did not differ among the subsequent clutches. Post-oviposition body mass, clutch size, and egg size showed differing degrees of annual variation, but clutch mass of either the first or the second clutch remained unchanged across the sampling years. The regression line describing the size–number trade-off was higher in the subsequent clutch than in the first clutch, but neither the line for first clutch, nor the line for the second clutch varied among years. Reproduction retarded growth more markedly in small females than in large ones. Our data show that: (1) trade-offs between size and number of eggs and between reproduction and growth (and thus, future reproduction) are evident in T. septentrionalis ; (2) females allocate an optimal fraction of accessible resources in current reproduction and to individual eggs; and (3) seasonal shifts in reproductive output and egg size are determined ultimately by natural selection.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 315–324.     

Anti-predator crèches and aggregations of ant-mimicking jumping spiders (Araneae: Salticidae)

Myrmarachne assimilis , an ant-like jumping spider (Araneae, Salticidae) from the Philippines and a Batesian mimic of Oecophylla smaragdina , the Asian weaver ant, aggregates on leaves in the company of its model. All stages in this species' lifecycle are sometimes found in nest complexes (nests connected to each other by silk). Although aggregating and forming nest complexes is known for a few other salticid species, the aggregations of M. assimilis have some unusual characteristics. In particular, reproductive females appear to be most frequently found with other reproductive females in nest complexes, suggesting that nest complexes have a role in parental care and are often built by females joining other females. An egg-survival experiment showed that eggs in solitary nests were more often destroyed than were eggs in nest complexes, suggesting that, for females of M. assimilis , choosing aggregations as oviposition sites may be functionally akin to life insurance for their progeny.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 475–481.     

Reproductive performance of a lacertid lizard at the core and the periphery of the species' range

The range boundaries of organisms are frequently interpreted in terms of a decline in the extent to which the life histories of outer populations are able to adapt to local environmental conditions. To test this hypothesis, we compared the reproductive characteristics of two Iberian populations of the lizard Psammodromus algirus (Linnaeus, 1758). One of them (Lerma) is close to the northern edge of the species' range, whereas the other one (El Pardo) occupies a typical core habitat 200 km further south. Gravid females were captured in the field and transported to the lab for egg laying. Second clutches were less frequent at Lerma (where clutch size and clutch mass were larger for first than for second clutches) than at El Pardo. The total mass of both clutches combined was similar at both sites. Thus, the higher frequency of second clutches at El Pardo appeared to balance the between-sites difference in energy allocation to the first clutch. Females from Lerma laid more but smaller eggs than those from El Pardo. When incubated at the same temperature, eggs from Lerma hatched sooner even when controlling for between-sites differences in mean egg size. These differences are interpreted in the light of the advantages of early hatching and high fecundity in the northern population, as opposed to large offspring size in the core population. We conclude that the life-history traits studied show enough variation, presumably of an adaptive nature, to cope with environmental challenges at the edge of the species' range.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 87–96.     

Clutch size manipulation, hatching success and offspring phenotype in the ball python (Python regius)

In a diverse array of avian and mammalian species, experimental manipulations of clutch size have tested the hypothesis that natural selection should adjust numbers of neonates produced so as to maximize the number of viable offspring at the end of the period of parental care. Reptiles have not been studied in this respect, probably because they rarely display parental care. However, females of all python species brood their eggs until hatching, but they do not care for their neonates. This feature provides a straightforward way to experimentally increase or reduce clutch size to see whether the mean clutch size observed in nature does indeed maximize hatching success and/or optimize offspring phenotypes. Eggs were removed or added to newly laid clutches of Ball Pythons ( Python regius ) in tropical Africa (nine control clutches, eight with 50% more eggs added, six with 42% of eggs removed). All clutches were brooded by females throughout the 2-month incubation period. Experimental manipulation of clutch-size did not significantly affect the phenotypes (morphology, locomotor ability) of hatchlings, but eggs in 'enlarged' clutches hatched later, and embryos were more likely to die before hatching. This mortality was due to desiccation of the eggs, with females being unable to cover 'enlarged' clutches sufficiently to retard water loss. Our results support the notion of an optimal clutch size, driven by limitations on parental ability to care for the offspring. However, the proximate mechanisms that generate this optimum value differ from those previously described in other kinds of animals. © 2003 The Linnean Society of London . Biological Journal of the Linnean Society 2003, 78 , 263–272.     

Evolution of South American mammalian predators (Borhyaenoidea): anatomical and palaeobiological implications

The evolution of South American carnivorous marsupials, the borhyaenoids, has been investigated through the functional analysis of postcranial adaptive traits and palaeobiological data. There is evidence that the evolutionary history of Borhyaenoidea proceeded from a noncursorial ancestor. The locomotion and habits of the early Palaeocene Mayulestes ferox probably approached a generalized plesiomorphic pattern for marsupial locomotion, i.e. primarily terrestrial with secondary arboreal adaptations. An exceptionally rich early Miocene Patagonian fauna has yielded various morphological predator types, from scansorial ambusher to terrestrial, incipiently cursorial, taxa. The most specialized borhyaenoid was the powerful sabretooth Thylacosmilus atrox that survived until the late Pliocene. The evolution from a scansorial pattern towards a cursorial trend, illustrated by Borhyaena tuberata , and towards the probable development of postlactational parental care in Thylacosmilus , required by its dental specialization and killing strategy, suggests a modification of the selective pressures and predatory activities of the group over evolutionary time.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 487–521.     

Mating distribution and its temporal dynamics affect operational sex ratio: a simulation study

The present study investigated how variation in mating distribution in time and among males influences the operational sex ratio (OSR) with a simulation inspired by paternally caring fish. Varying (1) the potential reproductive rate of each sex, (2) the mating distribution among males, and (3) the length of male mating phase, we created different mating patterns. In each case, we searched for the adult sex ratio that resulted in an OSR of 50% (where sex-roles switch). This approach enabled a comparison with a previous model. We found that the OSR was influenced by the distribution of matings in time and among males when the male mating phase was limited by a parental phase. Furthermore, the mating dynamics were shaped by the fact that the numbers of males and females and their capacities for collateral investment affected OSR immediately from the start of the reproductive season, whereas their times-out had a delayed effect on OSR.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 551–559.     

Male parental care and its adaptive significance in a neotropical frog

In the Puerto Rican frog Eleutherodactylus coqui, parental care is performed exclusively by males, and consists of attending the eggs and hatchlings at a terrestrial oviposition site. The two major behavioural components of parental care are egg brooding and nest defence against conspecific egg cannibals. Defence behaviour includes aggressive calling, biting, sustained biting, wrestling, and blocking directed against nest intruders. Parental care lasts from oviposition to hatching (17–26 days) and often for several days after hatching. During pre-hatching development, males are present in their nests 97.4% of the time during the day and 75.8% of the time at night. A large portion of this time is spent brooding eggs. In a field experiment, males were removed from their nests and the fate of clutches was monitored. Compared to control clutches (males not removed), experimental clutches had significantly lower hatching success and suffered significantly greater mortality from desiccation and cannibalism. Hence, parental care yields significant benefits to male fitness via increased offspring survival.     

Seasonal changes in the reproductive and life-history traits of Chrysomela populi L. (Coleoptera: Chrysomelidae)

Seasonal changes in the reproductive and life‐history traits of Chrysomela populi L. were investigated in Shobara (34°52′N, 133°01′E), Japan, in 2004 and 2005. Larvae were hatched and reared under natural photoperiod and temperature in 8 different periods between late April and early September in 2004. The incidence of adult diapause increased with progression of the season in 2004. The critical timing of diapause induction, as defined by 50% of females entering diapause, was estimated to occur between late July and early August. No effects of season on the survival rate from hatching to adult emergence, percentage ovipositing females and percentage females that deposited viable eggs were clearly detected. Adult weight at emergence fluctuated seasonally, which was probably caused by air temperature. No effect of season on the oviposition period was observed among females that averted diapause. Females that entered diapause in 2004 started oviposition from the first day of May in 2005. Reproductive output was significantly greater in diapause females than in non‐diapause females. This increase in the reproductive output of diapause females was caused by elongation of the oviposition period and consequently by enlargement of the number of egg clutches deposited. These results suggest that the seasonal timing of diapause induction in females of C. populi would be affected by various risks and benefits to reproduction and survival.     

Geographic variation in reproductive traits and trade-offs between size and number of eggs of the Chinese cobra (Naja atra)

We collected gravid Chinese cobras (Naja atra) from one island (Dinghai) and three mainland (Yiwu, Lishui and Quanzhou) populations in south‐eastern China to study geographical variation in female reproductive traits and the trade‐off between the size and number of eggs. We then conducted an common experiment on cobras from two of the four populations to further identify factors contributing to the observed trade‐offs. The mean size (snout–vent length) of the smallest five reproductive females increased with increasing latitude. Oviposition occurred between late June and early August, with females from the warmer localities laying eggs earlier than those from the colder localities. Maternal size was a major determinant of the reproductive investment in all populations, with larger females producing not only more but also larger eggs. Clutch size was more variable than egg size within and among populations. The observed geographical variation in clutch size, egg size, clutch mass and post‐oviposition body condition was not a simple consequence of variation in maternal size among populations, because interpopulation differences in these traits were still evident when the influence of maternal size was removed. The upper limit to reproductive investment was more likely to be set by the space availability in the island population, but by the resource availability in the three mainland populations. Trade‐offs between size and number of eggs were detected in all populations, with females that had larger clutches for their size having smaller eggs. Egg size at any given level of relative fecundity differed among populations, primarily because of interpopulation differences in the resource availability rather than the space availability. Except for the timing date of oviposition and the mean size of the smallest five reproductive females, all other examined traits did not vary in a geographically continuous trend. The common garden experiment, which standardized environmental factors, synchronized the timing date of oviposition, but it did not modify the conclusion drawn from the gravid females collected from the field. The observed geographical variation in the female reproductive traits could be attributed to the consequence of the effects of either proximate or ultimate factors. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 27–40.     

Obligate costs of parental care to offspring: egg brooding-induced hypoxia creates smaller, slower and weaker python offspring

Python egg brooding typifies parental care because it consists of multiple behaviours that provide for multiple developmental needs. For example, tightly coiling around the eggs benefits embryonic water balance, but periodic female postural adjustments improve embryonic gas exchange. Regardless of these postural adjustments, egg brooding creates a hypoxic intra-clutch environment that constrains embryonic metabolism. We further examined this novel and useful parental care model to determine: (1) any fitness-related costs of egg brooding to offspring; (2) whether any long-term costs are alleviated by postural adjustments. We artificially incubated Children's python ( Antaresia childreni ) clutches and modulated oxygen partial pressure ( P O₂) to create three treatments: normoxic (NRM, 20.3 kPa O₂), brooding [BRD, P O₂ profile typical of clutch P O₂ ( P O_2clutch) in maternally brooded clutches, 15.8–19.3 kPa O₂] and low (LOW, predicted P O₂ profile of maternally brooded P O_2clutch if females did not make postural adjustments, 14.4–18.6 kPa O₂). Using various metrics from ∼12 days pre-hatching to 14 days post-hatching, we demonstrated that NRM offspring were larger, faster and stronger than BRD offspring. As only hatchling heart mass differed between BRD and LOW treatments (LOW > BRD), postural adjustments may not alleviate hypoxia-related costs to embryos. Our results demonstrate that parental care may represent a compromise between competing developmental needs and thus entails obligate costs to the offspring.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 414–421.     

Seasonal monogamy and multiple paternity in a wild population of a territorial reptile (tuatara)

Investigating the mating system of a population provides insight into the evolution of reproductive patterns, and can inform conservation management of threatened or endangered species. Combining behavioural and genetic data is necessary to fully understand the mating system and factors affecting male reproductive success, yet behavioural data are often difficult to collect for threatened species. In the present study, we use behavioural data and paternity analyses to characterize the mating system of a high density population of a long-lived, ancient reptile (tuatara, Sphenodon punctatus ). We further investigate the phenotypic traits (including body size, body condition, tail length, and ectoparasite load) that affect male reproductive success. Our behavioural data reflect a seasonally monogamous system with low levels of polyandry and polygyny that are consistent with male mate guarding. Male reproduction is highly skewed (only 25–30% of males are successful), and body size is the primary predictor of male reproductive success. Based on the genetic data, multiple paternity was found in only 8% of clutches, and the results of the paternity analyses showed monandrous clutches from socially polyandrous females. Our behavioural and genetic results revealed complexities in female mating patterns that support the potential for cryptic female choice or sperm competition. This warrants further experimental investigation into the mechanisms underlying reptile fertilization and the disparities between social and genetic polyandry in wild populations.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 161–170.     

Time limitation affects offspring traits and female's fitness through maternal oviposition behaviour

Plasticity of various life‐history traits has evoked continuing interest among biologists. For example, the plasticity of offspring characteristics as well as maternal effects may be affected by time limitation and by limitation caused by changing environmental conditions. However, it is difficult to tell apart the effect of a time constraint, experienced by the mother, from food limitation, which is experienced by the offspring at the end of the season. In this study, we controlled for food limitation and simulated a time constraint for the mother. We tested how the seed beetle, Coccotrypes dactyliperda, adapts its reproductive investment after encountering a period of low availability of seeds as oviposition sites, as compared with females that encountered a seed at an early adult stage, while maintaining a similar food supply for offspring of both groups. We show that time limitation has a significant effect on the reproductive investment patterns of females. Females that were prevented from ovipositing, but provided with abundant food and later given oviposition sites, produced more, but smaller offspring than control females. Although the number of offspring increased, there was no indication of competition for food between offspring. We propose that, in order to compensate for the loss of time, mothers that experienced a shortage of oviposition sites influence their offspring to mature faster at the cost of a smaller than average body size. This study emphasizes the importance of considering more than one offspring generation in order to correctly estimate female fitness. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 728–736.     

Life-history, genotypic, and environmental correlates of clutch size in the Glanville fritillary butterfly

Abstract.  1. Glanville fritillary butterfly ( Melitaea cinxia ) females lay up to 10 clutches of 50–300 eggs in their lifetime. Clutch size is an important life-history trait as larval group size affects survival throughout larval development.
2. Two experiments were carried out in a large population cage in the field to investigate the life-history and environmental correlates of clutch size.
3. Clutch size decreased with the cumulative number of eggs laid previously, increased with both female body weight and the number of days between consecutive clutches.
4. Genotypic differences among females in the glycolytic enzyme phosphoglucose isomerase had a significant influence on clutch size, partly because females of particular genotypes were able to initiate oviposition earlier in the day and thereby take advantage of the most favourable environmental conditions for oviposition.
5. Factors influencing clutch size were partly different in two summers, indicating the modulating effect of prevailing environmental conditions on reproductive performance.     

Seasonal variation in genital and body size, sperm displacement ability, female mating rate, and male harassment in two calopterygid damselflies (Odonata: Calopterygidae)

Sperm competition is a pervasive force. One adaptation is the male ability to displace the rivals' sperm that females have stored from previous copulations. In the damselfly, Calopteryx haemorrhoidalis asturica , males with wider aedeagi displace more spermathecal sperm. The present study documents that the same mechanism operates in another damselfly, Hetaerina americana . However, this genital width in both species decreases along the season, but late-emerging females have more sperm displaced than early-emerging females. Because territorial males mated more and were larger in body and genital size than nonterritorial males, late-season females mated with considerably larger males with respect to female size and this produced higher sperm displacement. Assuming female benefits from storing sperm but that such benefit does not prevail if males displace sperm, it is predicted that, along the season, females will mate less and male harassment (in terms of male mating attempts and oviposition duration) will increase. These predictions were corroborated. In H. americana , it was also tested whether spermathecal sperm became less viable along the season. The results obtained did not corroborate this. This is the first evidence indicating that season affects sperm displacement ability and female mating frequency due to changes in male body and genital size.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 815–829.     

Functional ecological implications of intraspecific differences in wing melanization in Colias butterflies

Variation in the degree of insect wing melanin affects thermoregulation, and is expected to be adapted to local environmental conditions, for example over an elevational gradient. The effects of melanization on flight activity and egg maturation rate were assessed in the closely related butterflies Colias philodice eriphyle and C. eurytheme using experimental manipulation of wing darkness and transplant experiments between high and low elevation sites. Experimental manipulation of wing darkness in C. p. eriphyle demonstrated that light males had reduced flight activity at high elevations, and darkened males had reduced flight activity at low elevations. In contrast, the transplant experiments revealed asymmetrical adaptation for male C. p. eriphyle . At high elevations darker, high-elevation males had higher flight activity than lighter, low-elevation males, but there was no difference between the two groups at low elevation. For females, melanization had no effect on flight activity. However, an increase in female C. eurytheme wing darkness led to a significantly higher egg maturation rate at cold ambient temperatures, which may increase female reproductive output under natural conditions. Therefore, dispersers moving down in elevation may be more successful than those moving up.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 79–87.     

Multiple barriers to gene exchange in a field cricket hybrid zone

Data on patterns of variation within hybrid zones, combined with studies of life history, mate choice, and hybrid performance, allow estimates of the contribution of different pre-zygotic and post-zygotic barriers to reproductive isolation. We examine the role of behavioural barriers to gene exchange in the maintenance of a hybrid zone between North American field crickets Gryllus firmus and Gryllus pennsylvanicus . We consider these barriers in the context of previous studies that documented temporal and ecological isolation and a one-way post-mating incompatibility (i.e. G. firmus females do not produce offspring when they mate only with heterospecific males). Based on no-choice mating experiments in the laboratory, we demonstrate strong behavioural pre-mating barriers between the two species, but no apparent fecundity or fertility costs for G. firmus females when they mate with both conspecific and heterospecific males. Furthermore, we show that G. firmus females do not discriminate between hybrids and conspecifics, whereas G. pennsylvanicus females do. This observation could explain the asymmetric allele introgression observed in the hybrid zone. We also document a failure of heterospecific males to induce normal oviposition in G. firmus females, which may be due to rapid evolution of accessory gland proteins and may serve as an additional barrier to gene exchange.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 390–402.     

Life history and reproduction of the neotropical caecilian Siphonops annulatus (Amphibia,Gymnophiona, Siphonopidae), with special emphasis on parental care

Due to their mainly fossorial way of life, caecilian amphibians are the least known order of terrestrial vertebrates. Here, we present new observations on the natural history and reproductive biology of the neotropical oviparous, siphonopid caecilian Siphonops annulatus from a long-term study of this species in the field and in captivity. In the studied population, mating occurs between the end of August and beginning of October, and oviposition between November and December, when rainfall peaks. Egg hatching occurs between the end of December and beginning of January. The complete cycle of maternal care, from oviposition to independent, self-sufficient offspring lasts about 3 months. After eclosion, the altricial young feed on the mother's specially modified skin (maternal dermatophagy) and are also supplied by a fluid released from coming from the maternal cloaca. Also presented are observations on the burrows, feeding and social behaviour of S. annulatus.     

Fecundity compensation in the three‐spined stickleback Gasterosteus aculeatus infected by the diphyllobothriidean cestode Schistocephalus solidus

Causal explanations for host reproductive phenotypes influenced by parasitism fit into three broad evolutionary models: (1) non‐adaptive side effect; (2) adaptive parasitic manipulation; and (3) adaptive host defence. This study demonstrates fecundity compensation, an adaptive non‐immunological host defence, in the three‐spined stickleback fish (Gasterosteus aculeatus) infected by the diphyllobothriidean cestode Schistocephalus solidus. Both infected and uninfected female sticklebacks produced egg clutches at the same age and size. The reproductive capacity of infected females decreased rapidly with increased parasite : host body mass ratio. Body condition was lower in infected females than uninfected females and decreased with increasing parasite : host mass ratio. Females with clutches had greater body condition than those without clutches. A point biserial correlation showed that there was a body condition threshold necessary for clutch production to occur. Host females apparently had the capacity to produce egg clutches until the prolonged effects of nutrient theft by the parasite and the drain on resources from reproduction precluded clutch formation. Clutch mass, adjusted for female body mass, did not differ significantly between infected and uninfected females. Infected females apparently maintained the same level of reproductive allotment (egg mass as proportion of body mass) as uninfected females. Infected females produced larger clutches of smaller eggs than uninfected females, revealing a trade‐off between egg mass and egg number, consistent with the fecundity compensation hypothesis. The rapid loss of reproductive capacity with severity of infection probably reflects the influence of the parasite combined with a trade‐off between current and future reproduction in the host. Inter‐annual differences in reproductive performance may have reflected ecological influences on host pathology and/or intra‐annual seasonal changes. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Sexual selection for symmetrical male medflies (Diptera: Tephritidae) confirmed in the field

The role of fluctuating asymmetry as an indicator of fitness to females in mate choice remains controversial. Previous studies indicated that male medflies with symmetrical supra-fronto-orbital (SFO) bristles achieve relatively high mating success under laboratory conditions. Here we present data from field cage studies of wild collected medflies in Guatemala and Crete, which reveal the same association between fluctuating asymmetry in SFO bristle length and mating success as that seen in the laboratory. The experiments in Crete included males that were missing one or both of their bristles. A comparison of mating success between the three groups indicated that the mere presence of bristles did not exert a major influence. Analysis of attempted courtships suggests that the association between male mating success and FA in bristle length appears to be generated as a result of females being more likely to enter into courtships with symmetrical males, rather than through a rejection of asymmetrical males during or after it. This raises the possibility that the primary stimulus that makes a symmetrical male attractive is acting at too great a distance to depend on symmetry itself. Alternatives might include superior pheromone emissions or the occupation of a prime location within the lek.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81 , 347–355.