Shift in Egg-Laying Strategy to Avoid Plant Defense Leads to Reproductive Isolation in Mutualistic and Cheating Yucca Moths

Abstract

Through the process of ecological speciation, insect populations that adapt to new host plant species or to different plant tissues could speciate if such adaptations cause reproductive isolation. One of the key issues in this process is identifying the mechanisms by which adaptation in ecological traits leads directly to reproductive isolation. Here I show that within a radiation of specialist moths that pollinate and feed on yuccas, shifts in egg placement resulted in changes in female moth egg-laying structures that led to concomitant changes in male reproductive morphology. As pollinator moths evolved to circumvent the ability of yuccas to selectively abscise flowers that contain pollinator eggs, ovipositor length became shorter. Because mating occurs through the ovipositor, shortening of the ovipositor also led to significantly shorter and wider male intromittent organs. In instances where two pollinator moth species occur in sympatry and on the same host plant species, there is one short and one long ovipositor species that are reproductively isolated. Given that many plant-feeding insects lay eggs into plant tissues, changes in ovipositor morphology that lead to correlated changes in reproductive morphology may be a mechanism that maintains reproductive isolation among closely related species using the same host plant species. K E Y W O R D S :Adaptive radiation, ecological speciation, mutualism, reproductive isolation.Plant-feeding insects comprise at least one-third of the world's described biodiversity (Scheffers et al. 2012). Much of this diversity has been attributed to insect adaptation to novel host plant species or partitioning of host plants by tissue type that results in

Phylogenetic test of speciation by host shift in leaf cone moths (Caloptilia) feeding on maples (Acer)

“…Ecological shift within a host plant is also a significant process (Condon and Steck ; Cook et al. ; Joy and Crespi ; Althoff ; Mishima et al. ).…”

“…S1). Ecological shift within a host plant is also a significant process (Condon and Steck 1997;Cook et al 2002;Joy and Crespi 2007;Althoff 2014;Mishima et al 2014). For example, Zhang et al (2015) demonstrated divergence induced by host plant ages in sympatric sister beetles (Pyrrhalta maculicollis and Pyrrhalta aenescens) feeding on elm.…”

Diversification and coevolution in brood pollination mutualisms: Windows into the role of biotic interactions in generating biological diversity

“…The traits showing phenotype matching in this system (moth ovipositor length and plant ovary wall thickness) interact antagonistically, suggesting that to the extent that coevolution is implicated in speciation in brood pollination mutualisms, it may be through antagonistic coevolution as suggested by theoretical work (Yoder and Nuismer, 2010). Furthermore, Althoff (2014) suggested that, in Tegeticula, changes in ovipositor morphology led to correlated changes in male reproductive traits that could cause reproductive isolation among pollinator species. Thus, for yucca moths changes in antagonistic traits may have a direct link to speciation.…”

Patterns of host plant utilization and diversification in the brush-footed butterflies

“…The Oscillation Hypothesis was developed based on observations from the Nymphalidae (Insecta: Lepidoptera), where a positive correlation exists between species richness and host breadth (Janz et al ). This hypothesis has been widely cited and is often invoked (Wahlberg et al ; Condamine et al ; Kohyama et al ; Althoff ; Matos‐Maraví et al ; Marques et al ), however it has rarely been explicitly tested (Hardy and Otto ).…”