2nd August 11
(Photo credit)
A new study suggests that colour seems to affect female-female aggression in blue tits (pictured). It looks like females show more aggression to other females with similar levels of UV (ultraviolet) signals:-
Social and intrasexual competition for access to food, territory and reproduction is a major selection force acting on male phenotypes. In contrast, its evolutionary consequences for female phenotypes, especially female ornamentation, have been overlooked. Because fighting is costly for individuals, physical indicators of status that are correlated with aggressiveness or fighting ability are predicted to evolve. Under the badge of status hypothesis, individuals are predicted to attack unknown rivals that present signals of similar size or intensity more vigorously than dissimilar rivals. We used blue tits, Cyanistes caeruleus, to test whether UV/blue and yellow coloration mediates female aggression. We exposed territorial birds to two female blue tit decoys during nest building: one had a UV/blue crown with an enhanced UV signal (UV+) and the other had a reduced UV signal (UV−). We found that resident females with higher UV signal more often landed on the cage containing the UV+ decoys whereas females with a lower UV signal more often landed on the cage containing the UV− decoys. This result suggests that UV/blue crown coloration is a badge of status and supports the hypothesis that female–female competition can generate or maintain female ornamentation. Resident females with darker yellow chests also attacked the decoys with greater intensity. Previous studies suggest that brighter yellow females invest more inreproduction and consequently could be more sexually attractive. So, this last result may be explained by a higher motivation of darker yellow females or a trade-off between aggressiveness and female investment in reproduction.
(Animal Behaviour)
1st August 11
(Photo credit)
A recent study suggests they might.
Cheeky common cuckoos (pictured) lay eggs in other birds’ (host) nests, including nests of the reed warbler, which then raise their chicks for them. So, to maximise reproduction, it’s very likely that cuckoos try to improve access to these host nests.
One way they might do this is by mimicking predatory hawks. This might prevent aggressive ‘mobbing’ behaviour by potential hosts, giving the cuckoos better access to nests. A recent study has found evidence that this might be the case; that cuckoos might just be a “parasite in wolf’s clothing”:-
The reciprocal interactions between brood parasites and their hosts provide models for studying coevolution. For example, where hosts have evolved egg or chick discrimination, brood parasites have evolved mimicry of host eggs or chicks. Here, we suggest that there is another form of mimicry by cuckoos. A previous study has shown that naive small birds, with no evolutionary history of brood parasitism, are as afraid of adult common cuckoos Cuculus canorus as of sparrowhawks Accipiter nisus because of their physical resemblance. However, it has yet to be shown whether host species regard cuckoos as hawk like, or how hawk resemblance might benefit the cuckoo. We provide the first evidence that hawk resemblance involving barred underparts is an adaptive brood parasitic trait. We show by plumage manipulations of taxidermic models that reed warbler (Acrocephalus scirpaceus) hosts are more reluctant to approach and mob common cuckoos with barred rather than unbarred underparts. Our results indicate that reed warblers are more aggressive toward cuckoos that appear less hawk like and that hence, hawk resemblance facilitates access to host nests. Therefore, we suggest that cuckoos employ 2 forms of mimicry: To enhance parasitic laying, cuckoo adults are Batesian mimics of hawks, appearing dangerous to adult host survival, when in fact they could be safely attacked. At later stages, cuckoo eggs and chicks are aggressive mimics, appearing harmless but in fact dangerous to host reproduction. These strategies are each countered by host discrimination, providing the means for distinct coevolutionary arms races at successive stages of the host nesting cycle.
(Behavioral Ecology)
28th July 11
(Photo credit)
Yes; some fascinating new evidence suggests an orchid can mimic alarm pheromones of aphids to attract pollinating hoverflies (pictured):
Most insects are dependent on chemical communication for activities such as mate finding or host location. Several plants, and especially orchids, mimic insect semiochemicals to attract insects for unrewarded pollination. Here, we present a new case of pheromone mimicry found in the terrestrial orchid Epipactis veratrifolia. Flowers are visited and pollinated by several species of aphidophagous hoverflies, the females of which also often lay eggs in the flowers. The oviposition behaviour of these hoverflies is mainly guided by aphid-derived kairomones. We show that the flowers produce α- and β-pinene, β-myrcene and β-phellandrene, and that these compounds attract and induce oviposition behaviour in female hoverflies. This floral odour profile is remarkably similar to the alarm pheromone released by several aphid species, such as Megoura viciae. We therefore suggest that E. veratrifolia mimics aphid alarm pheromones to attract hoverflies for pollination; this is the first time, to our knowledge, that such a case of mimicry has been demonstrated.
(Proc. Roy. Soc. B)
13th May 11
(Photo credit)
Tent-building bats make and live in tents made out of leaves. A new study has found surprising results that more sociable species built more transient, ramshackle tents where as more non-sociable species built tents with more longevity:-
Although multiple hypotheses have been proposed to explain group formation, few fully explain the diversity of social interactions found in foliage-roosting bats. Among these bats, tent-roosting species are capable of constructing their own shelters. Although many bats utilize tents previously constructed by other species, it has been suggested that a particular subset of tent-roosting bats specialize on making tents from particular plant species. Tents provide protection from weather and often a place to roost close to foraging sites. Moreover, tent lifespan is plant species specific and may last from a few weeks to more than a year. To better understand effects that roosts have on social bonds of tent-roosting bats, we conducted a literature review to collect information on social systems and tent lifespan. We tested correlated evolution of group stability and group longevity with tent lifespan using Pagel’s method for discrete characters. We found that group stability and group longevity are correlated with tent lifespan. That there is correlated evolution between these characters contributes to our understanding of how different mechanisms interact to produce a variety of social systems in mammals.
(Biotropica)
