[HELICONIUS] Conference news and studies of H charithonia mating

[James Mallet]

Congratulations all the speakers and exhibitors 
at the recent Edmonton, Canada, Biology of 
Butterflies meeting. For more details see Chris Jiggins' blog:
<http://www.heliconius.org/2010/butterflies-on-the-prairies/>http://www.heliconius.org/2010/butterflies-on-the-prairies/ 


I think we'd all agree that the Heliconius talks 
at Edmonton about genomics and colour pattern 
genetics were exciting and interesting. Jiggins 
also discusses new findings on butterfly scent, 
including Catalina Estrada's work on anti-aphrodisiacs in Heliconius.

However, there's other interesting ecology and 
behavioural work going on that was not so well 
represented.  I especially liked these three 
papers (detailed below) just out on Heliconius 
charithonia pupal mating and mating behaviour.  I 
found Catalina Estrada's first paper especially 
interesting, as it showed how males search for 
larvae on the host plant, and identify them by 
odour, and also by means of odour of damaged host plant.

The authors are fully aware of the implications 
that males (as well as females) searching for 
host plants; this creates a pleiotropy of a host 
shift that can aid speciation via assortative 
mating as a "magic trait," and they discuss it extensively.

Larry Gilbert and I have both seen male 
Heliconius melpomene patrolling only near their 
host plants in Corcovado National Park, Costa 
Rica (where melpomene hosts and the butterfly 
itself are both rather rare), so the pleiotropic 
male host-searching behaviour is probably not 
limited to the pupal mating clade of 
Heliconius.  Such effects in non-pupal maters, 
however, await appropriate demonstration and 
experiments of the quality performed by Estrada 
and Gilbert, as well as Mendoza and Macías, in 
these studies on Heliconius charithonia.

Jim Mallet

Estrada, C., and L. E. Gilbert. 2010. Host plants 
and immatures as mate-searching cues in 
Heliconius butterflies. Animal Behaviour 80:231-239.
email: catalinaestra72 at hotmail.com, lgilbert at mail.utexas.edu
The study of interactions between phytophagous 
insects and their host plants extends beyond 
understanding how insects deal with plant 
chemical defences. Sexual behaviour of these 
herbivores is integrated in several ways with 
host plants, as the latter influence timing and 
location of reproduction, and can provide clues 
for finding mates. Nevertheless, while numerous 
studies link butterfly evolution to host plant 
adaptations, the influence of plants on butterfly 
sexual behaviour has been little studied. We 
conducted experiments to determine the role of 
host plant cues in mate-searching behaviour of 
Heliconius charithonia butterflies. This species 
exhibits precopulatory mate guarding behaviour, 
wherein males find and perch on pupae, then 
copulate with eclosing females ('pupal mating'). 
We found that males (1) visited plants damaged by 
feeding larvae more often than they visited 
undamaged plants and (2) displayed searching 
behaviour around the plant and in front of 
larvae, suggesting that odours signal the 
location of potential partners (pupae). Although 
males were attracted to common plant odours 
released after tissue damage, plants damaged by 
heterospecific butterfly larvae were less 
attractive, indicating that species recognition 
can occur at early life stages. Overall, our 
results suggest that host plants influence 
mate-searching behaviour of Heliconius. This 
might also be true for other species of 
butterflies with more conventional mating 
strategies, potentially contributing to the 
diversification of this group of phytophagous insects.

Mendoza-Cuenca, L., and R. Macías-Ordóñez. 2010. 
Female asynchrony may drive disruptive sexual 
selection on male mating phenotypes in a 
Heliconius butterfly. Behavioral Ecology 21:144-152.
email: lmendoza at lca.unam.mx
Alternative male phenotypes may be a source of 
novel adaptive traits and may evolve under strong 
sexual selection. We studied interpopulation 
differences in male mating behavior related to 
receptive female synchrony in the monandrous 
pupal-mating butterfly Heliconius charitonia. In 
the population in which female-receptive pupae 
were more synchronous, larger males were unable 
to monopolize mates; variance in male mating 
success was lower; strength of sexual selection 
was weak; and all males competed for access to 
female pupae using the same strategy (pupal 
mating). In the population where no more than one 
female was receptive at a time (extreme 
asynchrony), only large males competed for pupae, 
and among these, only the largest individuals 
successfully mated. Thus, variance in mating 
success was higher, and sexual selection within 
pupal maters was stronger. In this population, 
smaller males patrolled large areas as an 
alternative mating behavior. When unmated females 
were experimentally released, small male size was 
associated with higher mating success. We suggest 
that alternative patrolling behavior may have 
evolved under strong sexual selection as a 
consequence of high asynchrony in receptive 
female availability in some populations.

Estrada, C., S. Yildizhan, S. Schulz, and L. E. 
Gilbert. 2010. Sex-specific chemical cues from 
immatures facilitate the evolution of mate 
guarding in Heliconius butterflies. Proceedings 
of the Royal Society B-Biological Sciences 277:407-413.
email: catalinaestra72 at hotmail.com, lgilbert at mail.utexas.edu
Competition for mates has substantial effects on 
sensory systems and often leads to the evolution 
of extraordinary mating behaviours in nature. The 
ability of males to find sexually immature 
females and associate with them until mating is a 
remarkable example. Although several aspects of 
such pre-copulatory mate guarding have been 
investigated, little is known about the 
mechanisms used by males to locate immature 
females and assess their maturity. These are not 
only key components of the origin and maintenance 
of this mating strategy, but are also necessary 
for inferring the level to which females 
cooperate and thus the incidence of sexual 
conflict. We investigated the cues involved in 
recognition of immature females in Heliconius 
charithonia, a butterfly that exhibits mate 
guarding by perching on pupae. We found that 
males recognized female pupae using sex-specific 
volatile monoterpenes produced by them towards 
the end of pupal development. Considering the 
presumed biosynthetic pathways of such compounds 
and the reproductive biology of Heliconius, we 
propose that these monoterpenes are coevolved 
signals and not just sex-specific cues exploited 
by males. Their maintenance, despite lack of 
female mate choice, may be explained by variation 
in cost that females pay with this male behaviour 
under heterogeneous ecological conditions.

________________________________

James Mallet
UCL
www.ucl.ac.uk/taxome/jim  
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