Landscape‐scale life‐history gradients in New Zealand freshwater fish

Abstract

Summary Landscape‐scale clines in environmental parameters can lead to life‐history gradients. Study of interspecific life‐history differences can provide evidence of evolutionary adaptations in response to environmental cues, whereas examination of intraspecific life‐history variation can identify the ecological mechanisms driving trait evolution. We examined egg size and fecundity variation in three species of closely related freshwater fish (Galaxiidae) which occur across a habitat gradient in South Island, New Zealand. Inter‐population trait variation was assessed in the species with the widest distribution to investigate the ecological mechanisms driving egg size evolution. Substantial interspecific egg size and fecundity differences were observed. Galaxias paucispondylus, which generally occurs in high altitude headwater streams, showed an average egg size an order of magnitude larger, and fecundity an order of magnitude lower than G. brevipinnis, a species which rears in pelagic environments. Galaxias vulgaris, which rears fluvial environments but is generally distributed in lower catchment reaches than G. paucispondylus, showed intermediate fecundity and egg size traits. This interspecific trait variation is likely to be driven by differences in the larval rearing habitat, i.e. rearing in cold high altitude locations requires large well‐developed larvae (and therefore large eggs) but these come at the cost of maternal fecundity, whereas in rearing in warmer lower catchment watercourses, and pelagic habitats, does not require such large well‐developed larvae. Hence, fitness is maximised by progressively increasing fecundity by reducing egg size across this habitat cline. Life history‐habitat trends were repeated when intraspecific patterns in the widely distributed G. vulgaris were assessed, with population egg size increasing, and fecundity decreasing, in relation to a suite of interrelated environmental variables up an approximate altitudinal cline. The results highlight how inter‐ and intraspecific variation in egg size–fecundity trade‐offs in closely related species can interact to drive the evolution of landscape‐scale life‐history gradients. Egg size differences are likely to be driven by differences in the quality of the larval rearing habitat, i.e. rearing in a challenging habitat requires a larger egg whereas in relatively benign larval rearing habitat, fecundity can be maximised by reducing egg size. The interspecific variation observed provides evidence of trait adaptation in response to an environmental cue, while the intraspecific inter‐population differences indicate the potential ecological mechanisms driving trait evolution.

Effects of adoption of freshwater residency on life‐history ecology of terapontid grunters

“…Examples exist of intra‐specific variation and apparent trade‐offs in several of the key traits examined here (egg size, fecundity) in multiple fish clades, relating to environmental variation in a range of factors (e.g. flow and salinity regime, altitude, and temperature) (Closs et al, 2013; Jones et al, 2017; Kassen, Schluter, & McPhail, 1995; Morrongiello et al, 2012). Evidence also exists of flexibility in intra‐specific terapontid reproductive traits (spawning cues) relating to flow regime variation (Pusey et al, 2004), and phenotypic variation in response to different aspects of environmental variability in different catchment contexts are almost inevitable (but beyond the scope of the current study).…”

“…ecological opportunity and biogeographic events) are being increasingly documented (Betancur‐R et al, 2012; Bloom & Lovejoy, 2017; Davis, Unmack, Pusey, & Pearson, 2012; Davis, Unmack, Vari, & Betancur‐R, 2016a). The effects of these marine‐to‐freshwater transitions on the evolutionary trajectories of specific life‐history strategies and reproductive ecology within invading lineages, however, remain largely unstudied (although see Goto, 1990; Katoh & Nishida, 1994; VanGerwen‐Toyne et al, 2012; Closs, Hicks, & Jellyman, 2013; see Jones, Augspurger, & Closs, 2017 for studies contrasting diadromous versus freshwater residency). This relative paucity is perhaps surprising given that variation in life‐history strategy in freshwater fishes has been the focus of much theoretical and empirical research (see Winemiller & Rose, 1992).…”

“…Distributions of freshwater fishes across the scale of both the drainage basin and continent have been partly explained by these proposed matches between life‐history strategies and seasonality gradients in hydrological conditions. (Jones & Closs, 2015; Jones et al, 2017; Sternberg, Kennard, & Balcombe, 2014).…”

Life‐history variation along environmental and harvest clines of a northern freshwater fish: Plasticity and adaptation

“…Species inhabiting diverse environments across broad geographic ranges often display substantial life‐history clines (Armbruster, Bradshaw, Ruegg, & Holzapfel, ; Jones, Augspurger, & Closs, ; Morrison & Hero, ). Many of these species have characteristics (e.g.…”

Early life‐history adaptation influences conservation approaches for facultatively amphidromous fish

“…Fish eggs are sensitive to conditions such as temperature or desiccation (Dahlberg, ), and larvae tend to be small, fragile, and minimally provisioned (Chambers & Trippel, ; Dahlberg, ). As a result, early life history tends to be particularly vulnerable relative to later stages (Chambers & Trippel, ; Hjort, ), and it is a critical component for adapting or successfully matching to a new environment in the case of translocation for species conservation (Chambers & Trippel, ; Jones, Augspurger, & Closs, ; Jones & Closs, ; Winemiller, Fitzgerald, Bower, & Pianka, ). For example, if spawning times do not align with the environmental conditions required by eggs, or larvae are not correctly provisioned, recruitment will fail (Pankhurst & Munday, ).…”