Jalmenus evagoras, the imperial hairstreak or common imperial blue, is a small butterfly of the family Lycaenidae. It is found in Australia in the Australian Capital Territory, New South Wales, Queensland and Victoria.
Jalmenus eubulus was formerly considered a subspecies of Jalmenus evagoras.
The wingspan is about 40 millimetres (1.6 in).
Jalmenus evagoras exhibit an unusual mating system reflecting its close relationship with Iridomyrmex workers, commonly associating with Iridomyrmex anceps, Iridomyrmex vincinus and Iridomyrmex rufoniger. While butterfly larvae and pupae secrete food for the worker ants, the ants in return protect the organism from outside threats such as parasites and predators such as wasps, predatory ants, reduviid bugs, and spiders. This is an example of mutualism where both species work together, each benefiting in the process. Populations living without the presence of ants have a lower chance of survival. In mating, male Jalmenus evagoras learn the position of plants, taking into account the fact that healthy larvae and pupae are found in areas with attending ants.
Adult males search for mates by investigating the clusters of larvae clumped together on the branches of host plants such as the Acacia tree. The larvae feed on a various Acacia species, including Acacia falcata and Acacia spectabilis. Males hover around the juveniles, often using their antennae as a tool to taste for the age and sex of the larvae. A mating ball is subsequently formed as on average twenty males scramble to the site of an eclosing pupa that is just about to emerge as an adult. This competitive aggregation of males around the pupa is termed the explosive mating strategy. After a female emerges, copulation takes place right away, usually before she has a chance to let her wings harden and expand.
Female mating system and living
Female Jalmenus evagoras use hierarchical cues in oviposition, the egg laying process. Such cues include the appropriate host plant species, the nutritional quality of the plant, the presence or absence of attendant ants, and the presence or absence of conspecific juveniles. There is an interplay between these sets of cues that influences where a female decides to lay her eggs. To ensure that her eggs get the optimal chance of survival and reproduction later on, females prefer to lay eggs on high quality host plants, as these larvae can attract larger ant guards simply due to positioning. Female Jalmenus evagoras are monogamous. In experimentation it has been observed that females appear at a given site for shorter periods of time than males, although it is unknown if this is because females have a shorter life span or simply that they have emigrated out more. The shorter-life-span hypothesis is plausible given the fact that female Jalmenus evagoras are monogamous and do not necessarily need to live longer to mate with multiple mates.
Male mating system and living
Male Jalmenus evagoras exhibit protandry, usually emerging before females of the same species. In an effort to find mates, they regularly patrol trees containing pupae, taking into account the fact that healthy larvae and pupae are found in areas with attending ants. Only the healthy juvenile butterflies they are seeking live amongst the ants, and learning this cue serves as a way for male butterflies to find suitable females before they even mature, saving them both time and energy. Males are not territorial and will readily leave one host plant to join another mating ball. Males are sexually indiscriminate in mate searching, often resulting in attempted copulations with eclosing males. Female pupae are generally a bit larger than male pupae so size could in fact be used as an indicator of sex to avoid mistaken copulations. However, male Jalmenus evagoras do not depend on size and there is no evidence that they land on the bigger pupae, just the pupae that are tended to by more attendant ants. This shows the importance of the presence or absence of ants as a major factor in mate selection. In addition, males mate multiple times, and if they are successful, have been observed to mate as many as seven times in their lifetime. The three components of male lifetime mating success is longevity, encounter rate, and mating efficiency.
- "Jalmenus Hübner, 1818" at Markku Savela's Lepidoptera and Some Other Life Forms
- "2. Jalmenus evagoras (Donovan)". Australian Insect Common Names. Commonwealth Scientific and Industrial Research Organisation (Australia). 19 September 2004. Retrieved 2008-09-20.
- Costa, McDonald, Pierce (1996). "The effect of ant association on the population genetics of the Australian butterfly Jalmenus evagoras" (Biological Journal of the Linnean Society): 287–306.
- Kitching, Roger L. (1999). Biology of Australian Butterflies. pp. 279–314.
- Elgar, M. A.; Pierce, N. E. (1988). "Mating success and fecundity in an ant-tended lycaenid butterfly". Reproductive success: studies of selection and adaptation in contrasting breeding systems: 59–75.
- A. Wells, W. W. K. Houston (2001). Hesperioidea, Papilionoidea. Collingwood, Victoria: CSIRO Publishing. p. 264. ISBN 0-643-06700-0.
- Hughes, Chang, Wagner, Pierce (2000). "Effects of mating history on ejaculate size, fecundity, longevity, and copulation duration in the ant-tended lycaenid butterfly, Jalmenus evagoras". Behavioral Ecology and Sociobiology. 47 (3): 119–128. doi:10.1007/s002650050002.
- Clutton-Brock, T.H. (1988). Reproductive Success: Studies of Individual Variation in Contrasting Breeding Systems. pp. 60–70.
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