On the virtue of being the first born: the influence of date of birth on fitness in the mosquitofish, Gambusia affinis

Abstract

We found in an earlier study that mosquitofish (Gambusia affinis and G. holbrooki) ceased reproduction in the late summer, long before the end of warm weather, stored fat, then utilized reserves to survive the winter and initiate reproduction the following spring. We hypothesized that this pattern of fat utilization was a life history adaptation that enabled the fish to acquire food resources in the autumn then allocate them to reproduction the following spring when the fitness of the young would be greater. Here we evaluate one aspect of this hypothesis by evaluating the probability of survival to maturity and fecundity of young as a function of date of birth. We placed cohorts comprising eight to ten litters of young born early‐, mid‐ or late in the reproductive season in replicate field enclosures. The entire experiment was repeated in two different years. Early‐born young had a significantly higher probability of survival to maturity but did not differ in fecundity relative to the last cohort of the season. Early‐born young also attained maturity early enough to reproduce in their year of birth while late‐born young had to overwinter before reproduction. The fitness consequences to the mother of either producing one more litter of young at the end of the season, versus instead storing fat and reproducing the following spring are not as determinate as are the effects of date of birth on offspring fitness. Females most often gain fitness by not producing one last litter and instead over‐wintering. If, however, the overwinter survival of offspring is not influenced by their size at the end of the season, then a female's fitness could be enhanced by producing one more litter late in the season. If instead the probability of overwinter survival is strongly influenced by the size of offspring at the end of the season, then our results suggest that a female gains more by deferring reproduction and storing for overwinter survival and reproduction the following spring.

Life-history traits of the invasive fish Gambusia ­holbrooki in saline streams (SE Iberian Peninsula): Does salinity limit its invasive success?

“…This was earlier and faster in females, leading to higher average condition values than males. From July onwards, because of extreme reproductive effort (Reznick et al 2006), most 1+ individuals died after reproduction and the rest were only able to maintain their condition until winter. Alcaraz & García-Berthou (2007) observed that the somatic condition of Gambusia holbrooki females was lower in populations in high salinity conditions.…”

Life History Adaptations to Seasonality

“…A general benefit of capital breeding is that feeding is decoupled from breeding, with the possibility of breeding when the offspring have the highest value. In many seasonal environments peak offspring fitness is early in the feeding season (Nilsson 1999, Reznick et al 2006, favouring capital breeding. This is also predicted for the copepod studied here (P3, P4) where the ideal egg should be laid even prior to the feeding season.…”

Evolutionary consequences of predation: avoidance, escape, reproduction, and diversification

“…To date, few studies have examined shifts in reproductive timing in response to predator-induced mortality, although a number of examples are known for the effects of abiotic sources of mortality (e.g. desiccation, reduced energy sources due to winter; Thomson 1950;Lack 1954;Newman 1988;Brinkhof et al 1993;Van Noordwijk et al 1995;Reznick et al 2006b). Reproductive timing can also influence individual viability by minimizing negative effects of offspring production (e.g.…”