Fundamental and realized feeding niche breadths of sexual and asexual stick insects.

Chloé Larose,Tanja Schwander,Darren J Parker

doi:10.1098/rspb.2018.1805

Abstract

The factors contributing to the maintenance of sex over asexuality in natural populations remain unclear. Ecological divergences between sexual and asexual lineages could help to maintain reproductive polymorphisms, at least transiently, but the consequences of asexuality for the evolution of ecological niches are unknown. Here, we investigated how niche breadths change in transitions from sexual reproduction to asexuality. We used host plant ranges as a proxy to compare the realized feeding niche breadths of five independently derived asexual Timema stick insect species and their sexual relatives at both the species and population levels. Asexual species had systematically narrower realized niches than sexual species, though this pattern was not apparent at the population level. To investigate how the narrower realized niches of asexual species arise, we performed feeding experiments to estimate fundamental niche breadths but found no systematic differences between reproductive modes. The narrow realized niches found in asexual species are therefore probably a consequence of biotic interactions such as predation or competition, that constrain realized niche size in asexuals more strongly than in sexuals.

Highlights

The maintenance of obligate sex in natural populations, despite numerous disadvantages compared to other reproductive systems, is a major evolutionary paradox
Because asexual species derive from sexual ancestors, fundamental niches in new asexual species should depend directly upon the fundamental niche found in the ancestral sexual species
To assess potential interactions between colour polymorphism and the number of different host plant species used, and study the contribution of predation to the realized feeding niches, we compared the degree of colour polymorphism within Timema species and populations with their degree of ecological specialization

Summary

Introduction

The maintenance of obligate sex in natural populations, despite numerous disadvantages compared to other reproductive systems, is a major evolutionary paradox. We first estimated the size of the realized feeding niches of sexuals and asexuals both at the species and at the population level in five sexual– asexual Timema sister species pairs, using occurrences on different host plants in natural populations.

Results

Conclusion