Life-history plasticity in female threespine stickleback

Abstract

The postglacial adaptive radiation of the threespine stickleback fish (Gasterosteus aculeatus) has been widely used to investigate the roles of both adaptive evolution and plasticity in behavioral and morphological divergence from the ancestral condition represented by present-day oceanic stickleback. These phenotypes tend to exhibit high levels of ecotypic differentiation. Population divergence in life history has also been well studied, but in contrast to behavior and morphology, the extent and importance of plasticity has been much less well studied. In this review, we summarize what is known about life-history plasticity in female threespine stickleback, considering four traits intimately associated with reproductive output: age/size at maturation, level of reproductive effort, egg size and clutch size. We envision life-history plasticity in an iterative, ontogenetic framework, in which females may express plasticity repeatedly across each of several time frames. We contrast the results of laboratory and field studies because, for most traits, these approaches give somewhat different answers. We provide ideas on what the cues might be for observed plasticity in each trait and, when possible, we inquire about the relative costs and benefits to expressed plasticity. We end with an example of how we think plasticity may play out in stickleback life history given what we know of plasticity in the ancestor.

Iterative development and the scope for plasticity: contrasts among trait categories in an adaptive radiation

“…In contrast, in extreme limnetic populations, males typically court females in approaching groups and the diversionary display is not seen (Foster, 1994Foster and Baker, 1995). This pattern of ecotypic differentiation is apparent in behavior and morphology, but less so in life history, an issue we will address in the discussion (see also Baker et al, 2015).…”

“…However, there appears to be little within-season plasticity of clutch size in stickleback. Clutch size is tightly associated with reproductive effort (population level correlations range from 0.79-0.90 across 83 populations; Baker et al, 1998Baker et al, , 2008Baker et al, , 2015 and both are strongly influenced by female size. Once the effect of female size is removed, clutch size and egg size are inversely related, exhibiting expected trade-offs (Baker et al, 1998(Baker et al, , 2005Oravec and Reimchen, 2012).…”

“…Data from field collections indicate that in the majority of populations studied by Baker et al (2015), females increase their size-adjusted reproductive effort as they move through sequential breeding seasons. This suggests that females are not reproducing at maximum (though perhaps still very high) values early in life, likely enhancing the probability of surviving into future reproductive seasons, and that they allocate greater proportional resources to reproduction as the probability of surviving to another breeding season declines.…”

“…Thus, this pattern suggests iterative, adaptive developmental plasticity for this trait. Baker et al (2015) suggest that the clutch mass to body mass ratio of a given population can perhaps be viewed as the constitutive expression of reproductive effort-and that females modify this effort plastically as they enter a breeding season based on condition and environmental cues. This is an intriguing way of thinking about the interface between constitutive (heritable) contributions to populationspecific aspects of life history.…”

“…Thus, age and size of first reproduction is apparently an anciently plastic trait in the stickleback radiation. This plasticity is likely to have been favored in freshwater by the rather wide range of breeding dates within many populations, causing seasonally late-hatching individuals to delay reproduction for a year relative to those hatching early in the season (Saito and Nakano, 1999;Baker et al, 2015). As maturation is a onetime event, reversibility, or iteration are not relevant except in the sense that a female could potentially reproduce in 1 year and then skip reproduction in a later year (for example, Trippel and Harvey, 1989), although this seems unlikely in fish with lifespans that encompass only two breeding seasons (3 years of life) in most populations.…”