Comparative Population Genetic Structures and Local Adaptation of Two Mutualists

Abstract

Similar patterns of dispersal and gene flow between closely associated organisms may promote local adaptation and coevolutionary processes. We compare the genetic structures of the two species of a plant genus (Roridula gorgonias and R. dentata) and their respective obligately associated hemipteran mutualists (Pameridea roridulae and P. marlothi) using allozymes. In addition, we determine whether genetic structure is related to differences in host choice by Pameridea. Allozyme variation was found to be very structured among plant populations but less so among hemipteran populations. Strong genetic structuring among hemipteran populations was only evident when large distances isolated the plant populations on which they live. Although genetic distances among plant populations were correlated with genetic distances among hemipteran populations, genetic distances of both plants and hemipterans were better correlated with geographic distance. Because Roridula and Pameridea have different scales of gene flow, adaptation at the local population level is unlikely. However, the restricted gene flow of both plants and hemipterans could enable adaptation to occur at a regional level. In choice experiments, the hemipteran (Pameridea) has a strong preference for its carnivorous host plant (Roridula) above unrelated host plants. Pameridea also prefers its host species to its closely related sister species. Specialization at the specific level is likely to reinforce cospeciation processes in this mutualism. However, Pameridea does not exhibit intraspecific preferences toward plants from their natal populations above plants from isolated, non-natal populations.

Asymmetries in specialization in ant–plant mutualistic networks

“…the degree of nestedness). We already know from past studies of mutualism that species commonly differ geographically in the species with which they interact (Anderson et al 2004;Rudgers & Strauss 2004) and that some interactions coevolve as a geographic mosaic in which populations differ across landscapes in their adaptation and specialization to other species (Thompson 1994(Thompson , 2005. Hence, the problem to solve is whether interaction networks show similar patterns of specialization in different communities regardless of the particular species involved.…”

Comparative population genetic study of two oligophagous insects associated with the same hosts

“…A way to unravel the relative effects of intrinsic and extrinsic factors on the spatial structure of species is to develop a parallel study of multiple taxa associated with the same host(s) but showing contrasting patterns of host use. Yet, comparative genetic studies are still quite rare, and mostly involve closely related species (Brouat et al, 2003(Brouat et al, , 2004, or hosts and parasites or mutualists (Jobet et al, 2000;Anderson et al, 2004). We report on a comparative study of two insect species associated with the same hosts (xylophagous vs defoliator), each sampled following the same scheme and analysed with similar neutral markers, to assess the effects of both geographic isolation and host-plant availability on gene flow.…”

Locomotion in a sticky terrain

“…Recent coevolutionary studies on mutualistic interactions resulted in phylogenetic and geographical associations, suggesting cospeciation, coadaptation, and long-term coexistence in the Roridula-Pameridea complex (Anderson et al 2004;Anderson 2006). In host choice experiments with Roridula dentata L. (Roridulaceae) and Pameridea marlothi Poppius (Heteroptera, Miridae), bugs preferred host plants over unrelated host plant species and closely related sister species (Anderson et al 2004).…”

“…In host choice experiments with Roridula dentata L. (Roridulaceae) and Pameridea marlothi Poppius (Heteroptera, Miridae), bugs preferred host plants over unrelated host plant species and closely related sister species (Anderson et al 2004). The presence of an intermediate number of P. marlothi caused positive growth rates in R. dentata (Anderson and Midgley 2007).…”

“…The stronger build of P. roridulae may result in a larger muscle mass, due to which mirid bugs could generate stronger forces during locomotion on the sticky substrate, where they have possibly to free themselves from trichomes' viscous secretion. As a specialist species, it is strongly associated with its single host plant (Anderson et al 2004;Anderson 2006). Similar to related species of Miridae, they have to attach properly to the surface, not only during locomotion and feeding, but also during copulation, molting and oviposition of eggs into the plant tissue (Wheeler 2001).…”