Hybridization between endemic and widespread butterflies

Hybridization is an important evolutionary force. Climate warming is likely to change butterflies` emergence times and distributions, and could consequently lead to increased hybridization between sibling species that are now geographically separated. On the Mediterranean island of Sardinia we find the extraordinary situation that the widespread Meadow Brown butterfly Maniola jurtina overlaps distributionally with the endemic M. nurag. In the areas of overlap the two species hybridize. The genus Maniola includes two other island endemics, M. chia on the Greek island of Chios, and M. cypricola on Cyprus. These are not known to hybridize with M. jurtina. Females of all three endemics and the southern M. jurtina conduct a summer diapause. Successful oviposition after the diapause is crucial for the persistence of the respective population. The proposed study will investigate (I) Which factors limit hybridization between endemic and widespread Maniola? (II) Are endemic Maniola species ecologically more specialized than the widespread M. jurtina? (III) Which influence has climate warming on the summer diapause and survival of Maniola butterflies? Methodologically, the assessment of within-population genetic variation and admixture in the F1-generation will include the use of molecular markers like microsatellites and mtDNA sequences. Laboratory crosses will be carried out to experimentally investigate the degree of hybridization and the ecological factors differentiating the species. Chemical composition of pheromones will be analyzed to understand in how far pheromone-communication between species prevents hybridization. Breeding experiments will test the effect of temperature increase on the summer diapause and reproductive success of the butterflies. The proposed project builds on results obtained during the doctorate thesis of the applicant, and would be a continuation and deepening of the most intriguing questions that came up in earlier research. The study system, where endemic species and a widespread congeneric are separated, on the one hand along an ecological gradient, and on the other hand through isolation on islands, is quite unique. It promises to further our understanding of firstly species` differentiation despite hybridization, and secondly the effects of global warming on summer diapausing butterflies.

Hybridization and its role in speciation have been in the focus of my present FWF-funded research-project. That hybrid zones are accepted as probably very important for the formation of new species is a relatively new thought in speciation theory, at least for zoologists. New species were believed to mainly arise in geographic isolation from each other; or at least when there is restriction to gene flow between the populations, for example in island situations or when a population gets isolated at the top of a mountain. Now, we know that new species can arise also in the presence of gene flow, and this gene flow is most probably crucial. For speciation theory, this means that new species could arise, at least theoretically, from a pool of totally mixed individuals, which suddenly, maybe through ecological factors, start diverging into two or more distinguishable groups and remain distinct in sympatry also in the presence of substantial gene flow. This is a substantial shift in the philosophy of evolutionary thinking, bigger than apparent at first sight. Speciation in the presence of gene flow is about as far as you can get from speciation in geographic isolation. My emphasis lay in the study of intraspecific genetic, ecological and morphological variation in the butterfly genus Maniola. Also in these butterflies, gene flow does not hinder (ecological) differentiation, which one day could lead to the formation of new species. One of the most intriguing results of this project resulted from an experiment designed to test the reaction of females from different geographic provenance to prolonged summer conditions: Butterflies undergoing a summerly period of inactivity, one could call this a summer-sleep, have an extraordinary plasticity in aging. They can double or triple their life span in response to adverse environmental conditions. This finding could constitute the basis for further research into aging in insects and the role it might have in hybrid-speciation.