Experimental evidence of host race formation inMitourabutterflies (Lepidoptera: Lycaenidae)

Abstract

A population of herbivorous insects that shifts to a novel host can experience selection pressures that result in adaptation to the new resource. Host race formation, considered an early stage of the speciation process, may result. Th e current study investigates host shifts and variation in traits potentially involved in the evolution of reproductive isolation among populations of the juniper hairstreak butterfl y, Mitoura gryneus . Mitoura are closely associated with their host trees (Cupressaceae) and exhibit host plant fi delity: in addition to larval development and oviposition, host trees support male leks and mating. Female oviposition preference for the natal host, and diff erential fi tness of larvae when reared on natal versus alternate hosts, are indications that specialization and local adaptation to the natal host plant are occurring. Populations with single host plant associations ( Juniperus ashei , J. pinchotii and J. virginiana ) as well as populations with multiple hosts (both J. ashei and J. pinchotii ) were examined. Concordance between female preference and larval performance was found for J. ashei -associated populations. Population-level variation in the patterns of female preference and larval performance, both within and among host associations, may refl ect diff erences in the timing and direction of colonization of hosts. For a single nominal species that otherwise exhibits no morphological or phenological diff erences, the experimental assessment of specialization and host fi delity in M. gryneus provides strong support for the hypothesis of ongoing host race formation in these butterfl ies.

Comparison of plant preference hierarchies of male and female moths and the impact of larval rearing hosts

“…Matched plant preferences of males and females could thus provide a latent potential for disruptive natural selection combined with assortative mating (Caillaud andVia 2000, Downey andNice 2011) and, in the long run, sympatric speciation (Bolnick and Fitzpatrick 2007). This individual selective advantage could lead to accumulation of fitness differences on different host species.…”

“…This individual selective advantage could lead to accumulation of fitness differences on different host species. (Linn et al 2003, Bolnick andFitzpatrick 2007), Acyrthosiphon pisum (Via 1999), and lycaenid butterflies (Downey and Nice 2011). Polyphagy generally is not associated with host plant-linked reproductive isolation and evolutionary divergence (Jaenike 1990, Singer 2008.…”

“…(Linn et al 2003, Bolnick andFitzpatrick 2007) and the pea aphid Acyrthosiphon pisum (Via 1999). In contrast, for Lepidoptera, mate finding and host selection are generally considered more independent events, and consequently the main focus in host selection has been on female behavior (e.g., Olsson et al 2006, Moreau et al 2008, Downey and Nice 2011. Both systems have been investigated to elucidate possible mechanisms for sympatric speciation through host divergence.…”

One step ahead: a parasitoid disperses farther and forms a wider geographic population than its fig wasp host

“…The influence of host specificity on the genetic structure of insect herbivore populations appears inconsistent (Nason et al 2002;Ruiz-Montoya et al 2003;Downey & Nice 2011;Kohnen et al 2011). Similarly, host insect specificity is generally not a good indicator of the genetic structure of parasitoid populations, and the influence of herbivore host races on parasitoid population differentiation varies between systems (Vaughn & Antolin 1998;Jourdie et al 2010).…”

Lack of evolution in a leaf beetle that lives on two contrasting host plants

“…Numerous authors have celebrated how a shift between host plants can lead to a shift in mate preference as part of speciation (Bush 1969;Rice and Salt 1990;Feder et al 1994;Via 1999;Via et al 2000;Dr es and Mallet 2002;Geiselhardt et al 2009;Downey and Nice 2011). This can happen even in sympatry (Via 1999;Via et al 2000).…”