Paying for information: partial loads in central place foragers

Information about food sources can be crucial to the success of a foraging animal. We predict that this will influence foraging decisions by group-living foragers, which may sacrifice short-term foraging efficiency to collect information more frequently. This result emerges from a model of a central-place forager that can potentially receive information on newly available superior food sources at the central place. Such foragers are expected to return early from food sources, even with just partial loads, if information about the presence of sufficiently valuable food sources is likely to become available. Returning with an incomplete load implies that the forager is at that point not achieving the maximum possible food delivery rate. However, such partial loading can be more than compensated for by an earlier exploitation of a superior food source. Our model does not assume cooperative foraging and could thus be used to investigate this effect for any social central-place forager. We illustrate the approach using numerical calculations for honeybees and leafcutter ants, which do forage cooperatively. For these examples, however, our results indicate that reducing load confers minimal benefits in terms of receiving information. Moreover, the hypothesis that foragers reduce load to give information more quickly (rather than to receive it) fits empirical data from social insects better. Thus, we can conclude that in these two cases of social-insect foraging, efficient distribution of information by successful foragers may be more important than efficient collection of information by unsuccessful ones.     

Pairing patterns in relation to body size,genetic similarity and multilocus heterozygosity in a tropical monogamous bird species

The relative influence of genetic and phenotypic quality on pairing status and mating patterns in socially monogamous species remains poorly documented. We studied social status and pairing patterns in relation to genetic similarity and multilocus heterozygosity (MLH) estimates from 11 microsatellite markers, and both tarsus length and wing chord (as a measure of competitive ability in territorial defence) in a socially monogamous tropical bird species where individuals defend territories year-round, alone or in pairs, the Zenaida dove, Zenaida aurita. Tarsus length and wing chord did not differ between unpaired territorial birds and paired ones in either sex, whereas paired females, but not paired males, tended to be more heterozygous than unpaired ones. Among 84 pairs, we found no evidence for assortative mating for tarsus length, wing chord, MLH or genetic similarity. However, within pairs, male wing chord was positively related to female MLH and female tarsus length was positively related to male MLH, with no evidence for local effects, suggesting assortative mating by individual quality. Although the observed pattern of mating in Zenaida doves may be the product of mutual mate choice, further assessment of this hypothesis requires direct investigation of both mating preference in each sex and lifetime reproductive success in relation to body size and MLH.     

Why do house-hunting ants recruit in both directions?

To perform tasks, organisms often use multiple procedures. Explaining the breadth of such behavioural repertoires is not always straightforward. During house hunting, colonies of Temnothorax albipennis ants use a range of behaviours to organise their emigrations. In particular, the ants use tandem running to recruit naïve ants to potential nest sites. Initially, they use forward tandem runs (FTRs) in which one leader takes a single follower along the route from the old nest to the new one. Later, they use reverse tandem runs (RTRs) in the opposite direction. Tandem runs are used to teach active ants the route between the nests, so that they can be involved quickly in nest evaluation and subsequent recruitment. When a quorum of decision-makers at the new nest is reached, they switch to carrying nestmates. This is three times faster than tandem running. As a rule, having more FTRs early should thus mean faster emigrations, thereby reducing the colony’s vulnerability. So why do ants use RTRs, which are both slow and late? It would seem quicker and simpler for the ants to use more FTRs (and higher quorums) to have enough knowledgeable ants to do all the carrying. In this study, we present the first testable theoretical explanation for the role of RTRs. We set out to find the theoretically fastest emigration strategy for a set of emigration conditions. We conclude that RTRs can have a positive effect on emigration speed if FTRs are limited. In these cases, low quorums together with lots of reverse tandem running give the fastest emigration.