Butterfly-Ant Symbiosis
Many of the 6,000 species of the butterfly family Lycaenidae associate with ants. The complexity and beauty of such interactions in the Malaysian tropics attracted research on the subject. Lycaenid caterpillars may have special organs that attract and appease ants. Some species cannot survive without ants. For example, some lycaenid caterpillars are taken by ants into the nest and are allowed to eat ant larvae in exchange for a sweet secretion from the caterpillars. Some even evolve ant-like pheromones, so they pass as ants instead of invaders.
A Malaysian Blue caterpillar (Anthene emolus) can develop into an adult without the help of ants, but has a much greater risk of falling prey to predators and parasites. Female blues look for both host plants and Weaver Ants (Oecophylla smaragdina), laying eggs when the ants are present. Weaver Ants, a numerous and aggressive species of ants, offer caterpillars reliable protection. The ants transport young caterpillars around host plants to help them find food. In return, they "milk" the older larvae for a sweet secretion.
Emily Saarinen (graduate student, Entomology) traveled to Malaysia to research ant-caterpillar association. She discovered that different ant castes play different roles in tending caterpillars, and that major ants fight minor ants for the right to tend caterpillars. This defies standard theory that ants act in unity for the common good of the ant colony.
Chemical Ecology of Heliconius
Larvae of Heliconius butterflies feed exclusively on cyanide-producing passionvines. The caterpillars of this genus have developed the ability to counteract the effects of the cyanogenic glycosides in their Passiflora host plants, but the exact mechanisms for counteracting these cyanogens are unknown. Mirian Medina Hay-Roe focuses her research on the chemical interactions of Passiflora plants and their herbivores of the genus Heliconius. The investigation approaches insect/plant co-evolution at various levels. At the morphological level, she investigates genetic variation in life history characteristics, as well as, the influence of environmental factors (specifically, larval diet) and maternal effects. At the physiological level, her research investigates the fate of plant secondary compounds, the patterns of toxicity exhibited by Heliconius adults fed cyanogenic glycosides as caterpillars, and the mechanisms of detoxification used by the larvae. The evolutionary implication of her research focuses on an understanding of the evolution of mimicry rings based on plant toxicity.
Mimicry Diversiry, Evolution and Ecology of Ithomiine Communities
Ithomiines (see Systematics and Classification of Ithomiinae) dominate butterfly communities in neotropical forests, from sea level to over 2400m elevation. Ithomiines may comprise up to 50% of all butterflies in the forest understorey, and in many places up to 60 species fly together. Understanding how such diverse communities coexist is a central goal of evolutionary ecology, and ithomiines are an ideal study group. Ithomiine caterpillars feed almost exclusively on plants of the family Solanaceae, and each ithomiine species is usually confined to a single hostplant species. There is evidence of adaptive radiation, with more diverse plant clades supporting more diverse groups of ithomiines. Ithomiines are also notable for being unpalatable to predators and thus warningly colored, and extensively involved in mimicry rings. However, rather than all species converging on a single warning color pattern as predicted by mimicry theory, there are diverse complexes of mimetic species occurring together. Keith Willmott and Julia Robinson Willmott are thus working with colleagues from Edinburgh and Cambridge Universities, UK, to try to understand how mimicry diversity is maintained in two distinct ithomiine communities in eastern Ecuador.
Their hypothesis is that different mimicry complexes occur in different microhabitats (such as ridge tops or stream sides) where distinct predator species occur, so that predators rarely encounter more than one kind of colour pattern and thus the selection for convergence of different mimicry complexes is weak. The microhabitats where butterflies occur may be constrained by the microhabitats where their foodplants grow, so they are rearing ithomiines to identify hostplant usage. They are also mapping the height and microhabitat distribution of butterflies, plants and insectivorous birds to quantify niche space for these groups. Finally, they are deriving molecular and morphological phylogenies for certain ithomiine genera to test whether adaptive shifts in warning color pattern, hostplant or microhabitat have been important in speciation.
Learn more about Ithomiinae Immature stages.
Sound production in Heliconius butterflies
A few butterfly species have been reported to produce or hear sounds. The best-known example is the butterfly genus, Hamadryas, which produces loud clicks in flight. Mirian Medina Hay-Roe has discovered that Heliconius cydno also produces audible wing clicks during encounters with members of the same species and other Heliconius species. This finding suggests that wing clicks may play a role in intra- and interspecific communication in Heliconius. In collaboration with Richard Mankin (USDA), Mirian is trying to determine the evolutionary importance of sound production in the genus Heliconius.
Night Roosting in Heliconius
Communal roosting occurs when multiple insects of one or more species assemble in close proximity to one another for a certain period of time. Some species within the genus Heliconius display gregarious night roosting behavior. This particular behavior has been addressed several times over more than a century, but a explanation for it remains obscure. In order to better understand this behavior Christian Salcedo (Ph. D student) is studying clustering behavior and roost structure and patterns related to individual's sex, age, and size using Heliconius butterflies. This study is done with captive-bred colonies and utilizes unique facilities of the McGuire Center.
Speciation in Heliconius
Heliconius comprise a colorful and widespread butterfly genus distributed throughout the tropical and subtropical regions of the New World. These butterflies have been a subject of many studies due to their abundance and relative ease in breeding under laboratory conditions as well as due to the extensive mimicry that occurs in this group. Studying this model group is helping scientists to understand how species are formed and why they are so diverse.
Christian Salcedo (Ph. D student), has studied Heliconius sexual selection and speciation processes in Colombian species, Heliconius heurippa. This species is known to have an intermediate morphology and a hybrid genome, and in the study its intermediate wing color and pattern was recreated through laboratory crosses between H. melpomene, H. cydno, and their first generation hybrids (in Nature 2006 - see below). Mate preference experiments showed that the phenotype of H. heurippa is reproductively isolates it from both parental species. There is strong assortative mating between all three species, and in H. heurippa the wing pattern and color elements derived from H. melpomene and H. cydno are both critical for mate recognition by males.
NOTE: Nature 2006: Speciation by hybridization in Heliconius butterflies
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