Maximization of fitness by phenological and phenotypic plasticity in range expanding rabbitfishes (Siganidae)

Abstract

Global warming is modifying the phenology, life-history traits and biogeography of species around the world. Evidence of these effects have increased over recent decades; however, we still have a poor understanding of the possible outcomes of their interplay across global climatic gradients, hindering our ability to accurately predict the consequences of climate change in populations and ecosystems. We examined the effect that changes in biogeography can have on the life-history traits of two of the most successful range-extending fish species in the world: the tropical rabbitfishes Siganus fuscescens and Siganus rivulatus. Both species have established abundant populations at higher latitudes in the northern and southern hemispheres and have been identified as important ecological engineers with the potential to alter the community structure of seaweed forests (Laminariales and Fucales) in temperate regions. Life-history trait information from across their global distribution was compiled from the published literature and meta-analyses were conducted to assess changes in (i) the onset and duration of reproductive periods, (ii) size at maturity, (iii) fecundity, (iv) growth rates, (v) maximum body sizes and (vi) longevity in populations at the leading edge of range expansion in relation to sea surface temperature and primary productivity (a common proxy for nutritional resource levels). Populations at highest latitudes had shortened their reproductive periods and reduced growth rates, taking longer to reach sexual maturity and maximum sizes, but compensated this with higher fecundity per length class and longer lifespans than populations in warmer environments. Low primary productivity and temperature in the Mediterranean Sea resulted in lower growth rates and body sizes for S. rivulatus, but also lower length at maturity, increasing life-time reproductive output. The results suggest that plasticity in the phenology and life-history traits of range-expanding species would be important to enhance their fitness in high latitude environments, facilitating their persistence and possible further poleward expansions. Quantifying the magnitude and direction of these responses can improve our understanding and ability to forecast species redistributions and its repercussions in the functioning of temperate ecosystems.

Keywords: climate change; global warming; life-history traits; plasticity; rabbitfish; range-shifts; temperature-size-rule; tropicalization.

FIGURE 1

Sampling locations of information collected from the literature on reproduction (spawning and fecundity), growth rates, maximum length and longevity of Siganus rivulatus and Siganus fuscescens. Maximum body size information was also obtained from studies that included both reproduction and growth. Arrows indicate the direction of range expansion towards temperate environments

FIGURE 2

Period (continuous lines) and peak of spawning (arrows) with respect to sea surface temperature fluctuations (dashed lines; a, b), onset of annual spawning (c, d) and duration of spawning period (e, f) across minimum annual temperature in different climate regimes for the rabbitfish Siganus fuscescens and Siganus rivulatus. Error bands represent 95% confidence intervals of the regressions calculated with the function “predict” of the R package stats

FIGURE 3

Relationships between minimum length at maturity across minimum annual temperature (a, b) and fecundity (millions of eggs) and fork length interacting with climate (c, d) for the range‐extending rabbitfish Siganus fuscescens and Siganus rivulatus. Error bands represent 95% confidence intervals of the regressions derived from the function “predict” of the R package stats

FIGURE 4

von Bertalanffy growth curves (a, b), corresponding average length increments by age (c, d) and the effect of winter temperatures (e, f) and primary productivity (g, h) on growth rates across latitude as reported in the literature for the rabbitfish Siganus fuscescens and Siganus rivulatus in temperate, subtropical and tropical locations. Maximum age reported in the tropics in panel A was 3 y/o, further years represent predicted length. Error bands represent 95% confidence intervals of the regressions derived from bootstrapping using the R package nlstools for von Bertalanffy growth curves and the function “predict” of the R package stats for panels e–h

FIGURE 5

Relationships between maximum body size (a, b) and longevity (c, d) of the range‐expanding rabbitfish Siganus fuscescens and Siganus rivulatus with winter sea surface temperature in temperate, subtropical and tropical locations across their global distributions. Dashed lines in c and d represent quantile regression at the 90th percentile. Error bands represent 95% confidence intervals of the regressions derived from the function “predict” of the R package stats