Robustness of life histories to environmental variability in complex versus simple life cycles

Annie Jonsson

doi:10.1007/s12080-021-00501-1

Abstract

Most animal species have a complex life cycle (CLC) with metamorphosis. It is thus of interest to examine possible benefits of such life histories. The prevailing view is that CLC represents an adaptation for genetic decoupling of juvenile and adult traits, thereby allowing life stages to respond independently to different selective forces. Here I propose an additional potential advantage of CLCs that is, decreased variance in population growth rate due to habitat separation of life stages. Habitat separation of pre- and post-metamorphic stages means that the stages will experience different regimes of environmental variability. This is in contrast to species with simple life cycles (SLC) whose life stages often occupy one and the same habitat. The correlation in the fluctuations of the vital rates of life stages is therefore likely to be weaker in complex than in simple life cycles. By a theoretical framework using an analytical approach, I have (1) derived the relative advantage, in terms of long-run growth rate, of CLC over SLC phenotypes for a broad spectrum of life histories, and (2) explored which life histories that benefit most by a CLC, that is avoid correlation in vital rates between life stages. The direction and magnitude of gain depended on life history type and fluctuating vital rate. One implication of our study is that species with CLCs should, on average, be more robust to increased environmental variability caused by global warming than species with SLCs.

Highlights

The majority of animal species have complex life cycles (CLC) where individuals go through a metamorphosis involving a rapid and radical change in physiology, morphology, and ecology (Wilbur 1980; Werner 1988; Moran 1994; Truman and Riddiford 1999; Laudet 2011)
The most robust class of life histories, in terms of highest long-run growth rates are, as expected, complex life histories (CLCs), without a cost of metamorphosis, living in low variable habitats (Fig. 2). This result is due to the assumptions made in the model, a CLC will always have a higher long term growth rate compared with a corresponding simple life cycles (SLC); the magnitude of the benefit depends on the lifehistory and the amount of variation compared with SLC
The genetic decoupling hypothesis for the evolution of complex life cycles (Werner 1988; Ebenman 1992; Moran 1994; Aguirre et al 2014) and the “environmental decoupling” hypothesis proposed in the present work have one thing in common: the advantage of complex life cycles is that they lead to increased independence of the different life stages in the life cycle

Summary

Introduction

The majority of animal species have complex life cycles (CLC) where individuals go through a metamorphosis involving a rapid and radical change in physiology, morphology, and ecology (Wilbur 1980; Werner 1988; Moran 1994; Truman and Riddiford 1999; Laudet 2011). The prevailing view is that CLCs represent a response to widespread selection for developmental independence of different stages of the life cycle of species. Such independence permits adaptive evolution within a life cycle stage without correlated negative effects on traits of other stages (Werner 1988; Ebenman 1992; Moran 1994; Truman and Riddiford 1999; Aguirre et al 2014; Sherratt et al 2017). The adaptive decoupling hypothesis for the evolution of complex life cycles with metamorphosis is based on the assumption that traits expressed in pre-metamorphic and post-metamorphic stages should be at least partially

Methods

Results

Conclusion