Search results for "Reproductive value"
showing 7 items of 7 documents
Escaping the evolutionary trap: Can size-related contest advantage compensate for juvenile mortality disadvantage when parasitoids develop in unnatur…
2021
Abstract The quality of hosts for a parasitoid wasp may be influenced by attributes such as host size or species, with high quality for successful development usually coincident with high quality for larger offspring. This is not always the case: for the Scelionid wasp Trissolcus basalis, oviposition in eggs of the Brown Marmorated Stink Bug, Halyomorpha halys, rather than of the normal host, the Southern Green Stink Bug, Nezara viridula, leads to lower offspring survival, but survivors can be unusually large. Adult female T. basalis engage in contests for host access. As larger contestants are typically favoured in contests between parasitoids, the larger size of surviving offspring may co…
Sex-ratio and male sexual characters in a population of Blue tits Parus caeruleus
2005
Sex allocation theory proposes that parents should bias the sex ratio of their offspring if the reproductive value of one sex is greater than that of the other. In the monogamous blue tit (Parus caeruleus), males have a greater variance in reproductive success than females, and high-quality males have higher reproductive success than high-quality females due to extrapair paternity. Consequently, females mating with attractive males are expected to produce broods biased toward sons, as sons benefit more than daughters from inheriting their father’s characteristics. Song and plumage color in birds are secondary sexual characters indicating male quality and involved in female choice. We used t…
Fluctuating food supply affects the clutch size of Tengmalm's owl independent of laying date.
1991
In western Finland, yearly median laying dates of Tengmalm's owls varied from 14 March to 27 April during 1973–1989 and were negatively correlated with the winter densities of voles. Yearly mean clutch sizes varied from 4.0 to 6.7 and were more closely related to the spring than to the winter densities of voles. The yearly mean clutch size decreased with yearly median laying date. The 3-year vole population cycle is typical of the study area. The start of egg-laying was earliest in the peak phase of the cycle (median laying date 22 March), when vole numbers are high during egg-laying, but decline rapidly to low numbers in the next autumn or winter. In the increase phase (1 April) vole abund…
Dynamics of the caring family
2003
When several individuals simultaneously provide for offspring, as in families, the effort of any one individual will depend on the efforts of the other family members. This conflict of interest among family members is made more complicated by their relatedness because relatives share genetic interest to some degree. The conflict resolution will also be influenced by the differences in reproductive value between breeders and helpers. Here, we calculate evolutionarily stable provisioning efforts in families with up to two helpers. We explicitly consider that the behavioral choices are made in a life-history context, and we also consider how group sizes change dynamically; this affects, for ex…
Daphnia females adjust sex allocation in response to current sex ratio and density
2018
Cyclical parthenogenesis presents an interesting challenge for the study of sex allocation, as individuals’ allocation decisions involve both the choice between sexual and asexual reproduction, and the choice between sons and daughters. Male production is therefore expected to depend on ecological and evolutionary drivers of overall investment in sex, and those influencing male reproductive value during sexual periods. We manipulated experimental populations, and made repeated observations of natural populations over their growing season, to disentangle effects of population density and the timing of sex from effects of adult sex ratio on sex allocation in cyclically parthenogenetic Daphnia…
An experimental manipulation of life-history trajectories and resistance to oxidative stress
2006
Optimal investment into life-history traits depends on the environmental conditions that organisms are likely to experience during their life. Evolutionary theory tells us that optimal investment in reproduction versus maintenance is likely to shape the pattern of age-associated decline in performance, also known as aging. The currency that is traded against different vital functions is, however, still debated. Here, we took advantage of a phenotypic manipulation of individual quality in early life to explore (1) long-term consequences on life-history trajectories, and (2) the possible physiological mechanism underlying the life-history adjustments. We manipulated phenotypic quality of a co…
Patterns of cercarial production from Diplostomum spathaceum: terminal investment or bet hedging?
2004
In the production of the infective cercariae of trematodes, the terminal investment hypothesis of life-history theory predicts that the rate of host exploitation and cercarial production should increase during the period of cercarial shedding since the reproductive value of the parasite decreases during this period. In contrast, a bet hedging hypothesis that focuses on the success of transmission when host contact rate is variable predicts that cercarial production should decrease in an attempt to keep the host alive for longer and thus would increase the probability of successful transmission. We examined these two hypotheses under laboratory conditions and recorded the production ofDiplos…