Tanya Latty

Many biological systems use extensive networks for the transport of resources and information. Ants are no exception. How do biological systems achieve efficient transportation networks in the absence of centralized control and without global knowledge of the environment? Here, we address this question by studying the formation and properties of inter-nest transportation networks in the Argentine ant ( Linepithema humile ). We find that the formation of inter-nest networks depends on the number of ants involved in the construction process. When the number of ants is sufficient and networks do form, they tend to have short total length but a low level of robustness. These networks are topologically similar to either minimum spanning trees or Steiner networks. The process of network formation involves an initial construction of multiple links followed by a pruning process that reduces the number of trails. Our study thus illuminates the conditions under and the process by which minimal biological transport networks can be constructed.

How individuals deal with multiple conflicting demands is an important aspect of foraging ecology, yet work on foraging behavior has typically neglected neurologically simple organisms. Here we examine the impact of an abiotic risk (light) and energetic status on the foraging decisions of a protist, the slime mold Physarum polycephalum. We examined patch choice in a “non‐risky” environment by presenting starved and non‐starved P. polycephalum amoebas with a choice between two shaded food patches (one high quality, one low quality). We next examined patch choice in the presence of a conflict between foraging risk (light exposure) and food quality by presenting amoebas with a choice between a shaded, low‐quality patch, and a light‐exposed, high‐quality patch. When both patches were shaded, 100% of amoebas selected the higher quality food patch, irrespective of food‐quality differences or the individual's energetic status. When light exposure and food quality conflicted, amoebas selected the patch with the higher food quality when the quality difference between the patches was high. When the quality difference between patches was small, amoebas selected the shaded, lower quality patch.

1. Harem polygyny can have fitness benefits and costs on females. In bark beetles of the genus Ips the latter may include within‐harem competition between larvae. However, earlier competition between females for male care and mating opportunities may also influence oviposition behaviour. There has been relatively little investigation into the relationship between harem size and initial egg output. The present study investigated this relationship in the bark beetle Ips grandicollis . 2. The measure of egg output used was the number of eggs in the gallery with the most eggs in each harem. Mean (±SE) harem size of 242 observed harems was 3.25 ± 0.10. A curvilinear relationship was found between egg output and harem size, with females in smaller harems (one to four females) laying more eggs with increased harem size. However, females in larger harems (five to seven females) laid fewer eggs as harem size increased. The optimal harem size (in terms of number of eggs laid) was close to four females. 3. We found no evidence from a behavioural assay that females could preferentially choose unmated males over mated males with harems of two females. Additionally, the distribution of harem sizes suggests that females distribute themselves among males randomly. 4. The results suggest that harem size has effects on female reproduction that extend beyond larval competition and influence patterns of oviposition. The mechanism that determines why egg laying is greatest at intermediate levels is unknown. There is no evidence that smaller harems belong to lower quality males, but females may adjust egg‐laying behaviour in large harems as a result of reduced male attendance or anticipated larval competition.

Summary: In group‐living organisms, individuals that initiate aggregations, termed pioneers, may suffer higher mortality costs than individuals that join established aggregations. Here we examine the hypothesis that aggregation initiators achieve higher reproductive success in the early phases of colonization, potentially through lower competition and increased access to the resource (finder's advantage), and that this benefit is sufficient to outweigh the costs of pioneering. We also examine the role of arrival date (irrespective of order within the aggregation) on reproductive success, because individuals in seasonal environments may gain an advantage by arriving early. We test these hypotheses using mountain pine beetles, Dendroctonus ponderosae (Coleoptera: Curculionidae, Scolytinae), an obligately aggregating insect wherein pioneers suffer high mortality due to tree defences. We measured reproductive success at the start of winter when most components of final offspring number were likely to be determined. Surviving pioneers that successfully recruited conspecifics had smaller broods than individuals that joined aggregations, refuting our hypothesis. The later that a beetle settled within an aggregation, the higher its reproductive success. However, beetles that settled early in the season produced more offspring than those that settled later in the season, and this effect was generally stronger than settlement order within an aggregation. Our study highlights the importance of examining the effects of both settlement order and arrival date on the costs and benefits of pioneering aggregations.