The erect ‘penis’ is a flag of submission in a female-dominated society: greetings in Serengeti spotted hyenas

In East Africa, spotted hyenas live in large clans in a highly structured society dominated by females. A clan is a fission-fusion society where members are often solitary or in small groups. Spotted hyenas have a ritualized greeting during which two individuals stand parallel and face in opposite directions. Both individuals usually lift their hind leg and sniff or lick the anogenital region of the other. The unique aspect of greetings between individuals is the prominent role of the erect penis in animals of both sex. Female spotted hyenas have fused outer labiae and a pseudo-penis formed by the clitoris which closely resembles the male penis and can be erected. During greetings subordinates signalled submission with gestures which were not necessarily reciprocated by the dominant participant. Asymmetries were most pronounced in greetings between adult females where the probability of asymmetries increased with the divergence in rank between partners. Greetings between adult females and males were uncommon and restricted to males above median rank, principally the alpha male. Models of primate affiliative behavior assume that benefits derived from social relationships with different individuals are not equal and that individuals are selected to maximize the benefits they receive from social relationships with others. The observed distribution of greetings between partners of different rank matched the predictions of these models. An examination of non-adaptive hypotheses on the evolution of the pseudo-penis demonstrated that the conventional scenario linking (initial) virilization of female genitalia with selection for female dominance does not explain either the initial virilization, nor the evolution of the pseudo-penis to its current form and use. We sketch a new scenario that links (1) initial virilization to the occurrence of neonatal siblicide amongst members of a twin litter, and (2) costs of maintenance, pseudo-penile control over copulation and male submission. Our analysis confirms previous adaptive hypotheses on the function of the pseudo-penis in greetings and suggests new hypotheses to account for hitherto unexplained features. Correspondence to: M.L. East     

When is a male not a male? Sex recognition and choice in two sex-changing species

For dioecious species, choosing a mate of the same sex can have reproductive costs. For sex-changing animals, however, a lack of sex recognition may not carry a reproductive cost, as pairs that were initially same-sex can become opposite-sex pairs as one partner changes sex. The strength of sex discrimination in sex changers, then, should depend on the duration of mating associations and whether the time of sex change is influenced by social situation (“flexible” sex change). We studied two species of marine snails that change sex from male to female, one with flexible sex change and long-term or permanent mating associations (Crepidula fornicata) and one with short-term pairings and relatively fixed time of sex change (Crepidula convexa), to determine whether either species exhibits sex recognition and whether members of C. convexa show stronger sex discrimination. In laboratory experiments, small males, the choosing animals, were placed with either a male or a female conspecific (no-choice experiments) or given a choice of a male or female (choice experiments). We controlled for shell length in all experiments, as relative size may influence sex change or choice. Males of both species paired more often with females than males, but, as predicted, males of C. convexa showed stronger discrimination: When given a choice, no C. convexa male paired with another male. In contrast, some C. fornicata males always chose other males even when given the choice of a female. These results suggest that sex recognition can be adaptive even for sex changers but demonstrate that the level of sex recognition will depend on other aspects of reproductive behavior.     

Chelipeds are the real weapon: cheliped size is a more effective determinant than body size in male–male competition for mates in a hermit crab

To understand the evolution of weapons, we must understand both their functions and relative importance compared to body size in determining fighting success. Many decapod crustaceans develop disproportionately large chelipeds for their body size and use them as a weapon in agonistic interaction. There are, however, examples where weapons are merely signals of resource holding potential (RHP) and the RHP is actually determined by body size. We investigated the function and relative efficacy of body size and major cheliped size in male–male contests for females in the hermit crab Diogenes nitidimanus. Contests over females took two forms: (1) males preemptively guarded females and opponents did not fight with the guarding male. Cheliped size contributed significantly to the settlement of these contests and probably functioned as a visual signal for the opponents. (2) Guarding males engaged in physical combat with an opponent. In these cases, both body and cheliped sizes affected contest outcomes. The effect size for cheliped size was as strong, or stronger, than that for body size. These results suggest that large chelipeds have evolved as a true weapon and are effective in escalated fights for resources. Therefore they are also efficient visual signals for settling contests with only display. Our results are a rare example that clearly demonstrate that weapons are a more important determinant of fights than body size when both body and weapon size affect resource acquisition.     

Unravelling a ‘miner’s myth’ that environmental contamination in mining towns is naturally occurring

Australia has a long history of metal mining and smelting. Extraction and processing have resulted in elevated levels of toxic metals surrounding mining operations, which have adverse health effects, particularly to children. Resource companies, government agencies and employees often construct ‘myths’ to down play potential exposure risks and responsibility arising from operating emissions. Typical statements include: contaminants are naturally occurring, the wind blows emissions away from residential areas, contaminants are not bioavailable, or the problem is a legacy issue and not related to current operations. Evidence from mining and smelting towns shows that such ‘myths’ are exactly that. In mining towns, the default and primary defence against contamination is that elevated metals in adjacent urban environments are from the erosion and weathering of the ore bodies over millennia—hence ‘naturally occurring’. Not only is this a difficult argument to unravel from an evidence-based perspective, but also it causes confusion and delays remediation work, hindering efforts to reduce harmful exposures to children. An example of this situation is from Broken Hill, New South Wales, home to one of the world’s largest lead–zinc–silver ore body, which has been mined continuously for over 130 years. Environmental metal concentration and lead isotopic data from soil samples collected from across Broken Hill are used to establish the nature and timing of lead contamination. We use multiple lines of evidence to unravel a ‘miner’s myth’ by evaluating current soil metal concentrations and lead isotopic compositions, geological data, historical environmental assessments and old photographic evidence to assess the impacts from early smelting along with mining to the surface soils in the city.     

Cultivated land – a scarce commodity in a densely populated rural area in South Wollo,Ethiopia

Cultivated and settlement areas were studied in a small area (14 km2) in South Wollo, Ethiopia, by aerial photos, satellite images, field observations and interviews. Areas for cultivation/rural settlement decreased a few per cent between 1958 and 2013. Cultivated land per household slowly decreased in 1958–2003 but in 2003–2013 the annual decrease was 3–4 times higher. New farm buildings are often built on cultivated land, and abandoned buildings areas return to cultivation. Rainwater harvesting ponds have increased the areas with perennial crops that are important as a source of income. Tin roofed buildings are signs of improved livelihood. Very small farm size and rain-dependent agriculture combined with climate variability make food security vulnerable. Land-use inventories including remote sensing and local knowledge would be a valuable approach to assess livelihood needs. Further, it should involve decision makers at different levels, but local agricultural extension officers may play a central role.     

How do larvae attach to a solid in a laminar flow?

A hydrodynamic model explaining the mechanism of contact of marine larvae in vertical flows is presented. Two hydrodynamic factors—flow vorticity and larval self-propulsion—are the key components in the mathematical model. It is shown that flow vorticity causes a larva to rotate and change the direction of self-thrust, thus leading to its migration across the mean flow. The latter motion is of an oscillatory nature. Contact will be enabled only for sufficiently large amplitudes of oscillations. Simple expressions for the probability of initial contact are obtained for two-dimensional Couette and Poiseuille flows. The three-dimensional motion of a larva in a tube is studied using the Monte-Carlo simulations. It is shown that contact probability depends mainly on the ratio of the characteristic flow velocity and the larva’s swimming speed. The theoretical results compare favorably with available experimental data. Possible applications of the method and results presented here to the classical problem of larval attachment to bodies of general geometry are briefly discussed in the concluding section.     

Human–wildlife coexistence in a changing world

Human–wildlife conflict (HWC) is a key topic in conservation and agricultural research. Decision makers need evidence-based information to design sustainable management plans and policy instruments. However, providing objective decision support can be challenging because realities and perceptions of human–wildlife interactions vary widely between and within rural, urban, and peri-urban areas. Land users who incur costs through wildlife argue that wildlife-related losses should be compensated and that prevention should be subsidized. Supporters of human–wildlife coexistence policies, such as urban-dwelling people, may not face threats to their livelihoods from wildlife. Such spatial heterogeneity in the cost and benefits of living with wildlife is germane in most contemporary societies. This Special Section features contributions on wildlife-induced damages that range from human perspectives (land use, psychology, governance, local attitudes and perceptions, costs and benefits, and HWC and coexistence theory) to ecological perspectives (animal behavior). Building on current literature and articles in this section, we developed a conceptual model to help frame HWC and coexistence dimensions. The framework can be used to determine damage prevention implementation levels and approaches to HWC resolution. Our synthesis revealed that inter- and transdisciplinary approaches and multilevel governance approaches can help stakeholders and institutions implement sustainable management strategies that promote human–wildlife coexistence.     

Look before you leap: is risk of injury a foraging cost?

Theory states that an optimal forager should exploit a patch so long as its harvest rate of resources from the patch exceeds its energetic, predation, and missed opportunity costs for foraging. However, for many foragers, predation is not the only source of danger they face while foraging. Foragers also face the risk of injuring themselves. To test whether risk of injury gives rise to a foraging cost, we offered red foxes pairs of depletable resource patches in which they experienced diminishing returns. The resource patches were identical in all respects, save for the risk of injury. In response, the foxes exploited the safe patches more intensively. They foraged for a longer time and also removed more food (i.e., had lower giving up densities) in the safe patches compared to the risky patches. Although they never sustained injury, video footage revealed that the foxes used greater care while foraging from the risky patches and removed food at a slower rate. Furthermore, an increase in their hunger state led foxes to allocate more time to foraging from the risky patches, thereby exposing themselves to higher risks. Our results suggest that foxes treat risk of injury as a foraging cost and use time allocation and daring—the willingness to risk injury—as tools for managing their risk of injury while foraging. This is the first study, to our knowledge, which explicitly tests and shows that risk of injury is indeed a foraging cost. While nearly all foragers may face an injury cost of foraging, we suggest that this cost will be largest and most important for predators.     

How unpredictable is the individual scanning process in socially foraging mammals?

In group-forming prey species, theory assumes that individuals within groups should scan independently of one another, with vigilance sequences being relatively unpredictable, making interscan durations highly variable. We attempted to detect any divergence from randomness in the scanning process in three mammalian prey species phylogenetically and geographically separated and exposed to different levels of predation: waterbuck, Kobus ellipsiprymnus defassa, under a high observed predation risk, eastern grey kangaroo, Macropus giganteus, still experiencing occasional predation and European roe deer, Capreolus capreolus, under a very low natural predation risk. Our results revealed that the focal interscan duration increased when the duration of the preceding interscan increased, whatever the studied species and the predation risk that its individuals experienced, and decreased with the preceding scan duration in two species under, respectively, occasional and low predation risks. The exponential distribution was the tested model that fitted the observed distributions of interscan durations least well. We discuss what can trigger non-randomness in scanning, through a non-homogenous Poisson process, at both intra-individual and inter-individual levels, particularly with regard to previous studies that have demonstrated synchronisation of vigilance in such mammals. Our results suggest the need to reconsider any assumption of randomness in scanning in the basic model predicting form and frequency of scanning behaviour by prey species.     

How is activity distributed among and within tasks in Temnothorax ants?

How social insect colonies behave results from the actions of their workers. Individual variation among workers in their response to various tasks is necessary for the division of labor within colonies. A worker may be active in only a subset of tasks (specialist), perform all tasks (elite), or exhibit no particular pattern of task activity (idiosyncratic). Here we examine how worker activity is distributed among and within tasks in ants of the genus Temnothorax. We found that workers exhibited elitism within a situation, i.e., in particular sets of tasks, such as those associated with emigrations, nest building, or foraging. However, there was weak specialization for working in a particular situation. A few workers exhibited elitism across all situations, i.e., high performance in all tasks in all situations. Within any particular task, the distribution of activity among workers was skewed, with few ants performing most of the work and most ants performing very little of the work. We further found that workers persisted in their task preference over days, with the same individuals performing most of the work day after day. Interestingly, colonies were robust to the removal of these highly active workers; they were replaced by other individuals that were previously less active. This replacement was not short-lived; when the removed individuals were returned to the colony, not all of them resumed their prior high activity levels, and not all the workers that replaced them reduced their activity. Thus, even though some workers specialize in tasks within a particular situation and are persistent in performing them, task allocation in a colony is plastic and colonies can withstand removal of highly active individuals.     

Nanotechnology in cosmetics: a boon or bane?

Recent advances in the field of nanotechnology enabled the manufacturing of elaborated nanometer-sized particles for various biomedical applications. The cosmetic industry is one of the most enthusiastic early adopters of nanotechnology which routinely uses nano-scale ingredients. However, in the absence of mandatory product labeling, it is difficult to estimate the number of cosmetics, sunscreens and personal care products containing nanoparticles that are now commercially available. The increased capacity of nanoparticles to penetrate skin and gain access to human cells is a double-edged sword as it may be useful for medical purposes, but might also result in far greater uptake of substances that exert adverse health effects. Since nanomaterials represent a large group of structurally, physically, and chemically variable substances, specific toxicological studies are required for each product prior to commercialization. This review aims to delineate the most investigated applications, risk and safety considerations, and regulation of nanotechnology in the field of cosmetics.     

Threshold management in a coupled economic–ecological system

Economic analysis of optimal ecosystem management in the presence of a threshold has typically ignored the potential for induced behavioral responses. This paper contributes to the literature on non-convex ecosystem management by considering the implications of a particular behavioral response in a regional economy – that of amenity-led growth – to changes in ecosystem services generated by a lake ecosystem subject to a eutrophication threshold. The essential policy challenge is to achieve optimal levels of lake nutrients and urbanization given that improvements to water quality will induce additional migration and urbanization in the region with attendant ecological impacts. We show that policies that ignore the recursive relationship between urbanization and water quality unintentionally exacerbate boom-bust cycles of regional growth and decline and risk pushing the system towards long-run economic decline. In contrast, the optimal policy accounts for the behavioral feedbacks to improved ecosystem services, and balances regional growth and ecological degradation.     

Issues in information theory-based statistical inference—a commentary from a frequentist’s perspective

After several decades during which applied statistical inference in research on animal behaviour and behavioural ecology has been heavily dominated by null hypothesis significance testing (NHST), a new approach based on information theoretic (IT) criteria has recently become increasingly popular, and occasionally, it has been considered to be generally superior to conventional NHST. In this commentary, I discuss some limitations the IT-based method may have under certain circumstances. In addition, I reviewed some recent articles published in the fields of animal behaviour and behavioural ecology and point to some common failures, misunderstandings and issues frequently appearing in the practical application of IT-based methods. Based on this, I give some hints about how to avoid common pitfalls in the application of IT-based inference, when to choose one or the other approach and discuss under which circumstances a mixing of the two approaches might be appropriate.     

“Anting” in Blue Jays: evidence in support of a food-preparatory function

Summary.  Anting, the plumage-dipping behavior to which ants (mostly formicines) are commonly subjected by birds (mostly passerines), is shown in tests with hand-raised Blue Jays (Cyanocitta cristata) and the ant Formica exsectoides to be instinctive: the birds displayed typical renditions of the behavior on the first occasion that they encountered ants. Evidence is presented supportive of the view that anting is a strategy by which birds render ants fit for ingestion. Formicine ants are ordinarily protected by their formic acid-containing spray. Being wiped into the bird’s plumage causes them to discharge that spray, without harm to the bird, to the point of almost total emptying of the glandular sac in which the secretion is stored. The ants are therefore essentially secretion-free by the time they are swallowed. Further evidence indicates that it is the ant’s possession of the acid sac that triggers the anting behavior in the bird. If F. exsectoides are surgically deprived of their acid sac, they are eaten by the birds without first being subjected to anting. Data are also presented indicating that the ant’s crop, which is especially capacious in formicines (its contents may amount to over 30% of the formicine’s mass), and which appears to survive the anting procedure intact, constitutes, at least when laden, a valuable component of the trophic package that the bird accesses by anting.     

Short retention times of stomach temperature loggers in free-living seabirds: is there hope in the spring?

Stomach temperature loggers have proved useful for the study of feeding activity in free-living seabirds, but their usage has been restricted because they are frequently dislodged and lost during the seabirds' regular regurgitation of indigestible prey remains. In the present study we examine the incidence of spontaneous regurgitation (pellet production) in free-living seabirds, consider the effect this has on the likely retrieval of stomach temperature loggers and present a structural modification of the logger housings which leads to a much lower incidence of regurgitation. Systems were tested on albatrosses, cormorants, gannets and penguins. Received: 15 July 1997 / Accepted: 31 October 1997     

Acoustic ranging in poison frogs—it is not about signal amplitude alone

Behavioral Ecology and Sociobiology - Colony size is an important predictor of annual survival and reproduction in social insects. By tracking monthly forager turn over, we measured the...     

Why is dominance hierarchy age-related in social insects? The relative longevity hypothesis

In temperate regions, older eusocial hymenopteran females with annual life cycles (annual-temperate) tend to dominate younger females, a behavior demonstrated by many Polistes. However, in queenless ponerine ants and primitively eusocial tropical wasps (perennial/tropical), a younger female can be dominant and occasionally takes over from the older, most dominant reproductive female, the alpha. We investigated these patterns using an inclusive fitness model. The most important difference between the above two cases lay in the length of individual life compared with colony life. Colonies dissolve before winter in the annual-temperate case, so the expected future tenure of the replacement alpha is never longer than that of the original alpha. This makes the non-reproductive subordinate tactic more advantageous for individuals that emerge later in the season because of the fitness cost of superseding. The perennial/tropical case does not have a clear upper limit for colony longevity, so the model predicts that late-born younger daughters are more likely to challenge their mother-alpha because of the expected long future tenure of the new alpha compared with the small indirect cost of the mothers reproductive failure. To switch tactics from being a subordinate to being the new alpha is only optimal in some situations. The high mortality rate of subordinate workers does not qualitatively alter the above pattern. The specific sexual production schedule of the colony sometimes affects the optimal behavior of females in the perennial/tropical case, and older individuals can dominate younger ones when the end of current round of sexual production is imminent.Electronic Supplementary Material Supplementary material is available for this article at     

Water budget and the consequent duration of canopy carbon gain in a teak plantation in a dry tropical region: Analysis using a soil–plant–air continuum multilayer model

A soil–plant–air continuum multilayer model was used to numerically simulate canopy net assimilation (A_n), evapotranspiration (ET), and soil moisture in a deciduous teak plantation in a dry tropical climate of northern Thailand to examine the influence of soil drought on A_n. The timings of leaf flush and the end of the canopy duration period (CDP) were also investigated from the perspective of the temporal positive carbon gain. Two numerical experiments with different seasonal patterns of leaf area index (LAI) were carried out using above-canopy hydrometeorological data as input data. The first experiment involved seasonally varying LAI estimated based on time-series of radiative transmittance through the canopy, and the second experiment applied an annually constant LAI. The first simulation captured the measured seasonal changes in soil surface moisture; the simulated transpiration agreed with seasonal changes in heat pulse velocity, corresponding to the water use of individual trees, and the simulated A_n became slightly negative. However, in the second simulation, A_n became negative in the dry season because the decline in stomatal conductance due to severe soil drought limited the assimilation, and the simultaneous increase in leaf temperature increased dark respiration. Thus, these experiments revealed that the leaflessness in the dry season is reasonable for carbon gain and emphasized the unfavorable soil water status for carbon gain in the dry season. Examining the duration of positive A_n (DPA) in the second simulation showed that the start of the longest DPA (LDPA) in a year approached the timing of leaf flush in the teak plantation after the spring equinox. On the other hand, the end appeared earlier than that of all CDPs. This result is consistent with the sap flow stopping earlier than the complete leaf fall, implying that the carbon assimilation period ends before the completion of defoliation. The model sensitivity analysis in the second simulation suggests that a smaller LAI and slower maximum rate of carboxylation likely extend the LDPA because soil water from the surface to rooting depth is maintained longer at levels adequate for carbon gain by decreased canopy transpiration. The experiments also suggest that lower soil hydraulic conductivity and deeper rooting depth can postpone the end of the LDPA by increasing soil water retention and the soil water capacity, respectively.     

Sex-biased dispersal in a long-lived polygynous reptile (Crocodylus johnstoni )

We compared natal dispersals of freshwater crocodiles (Crocodylus johnstoni) against the prediction of male dispersal bias for a polygynous mating system. The crocodiles inhabited a linear series of pools and we calculated the net distances from natal pools to recapture locations some 12–18 years later, at maturity. Philopatry was assessed in terms of adult social distances. A female social distance was 0.46 pools and a male social distance was 1.0 pool. By these criteria, both sexes showed low levels of philopatry (7–12%). However, individuals of both sexes dispersed from the natal site long before they were sexually mature. Divergence in dispersal patterns by sex occurred after the maturity threshold, as males dispersed two to three times farther than females. Intrasexual competition by males is resolved by a size-based hierarchy. The displacement of small males from local mating access is a probable cause of the longer dispersals undertaken by males. Competition, rather than inbreeding avoidance, is driving dispersal in this population of freshwater crocodiles. Received: 8 May 1998 / Accepted after revision: 26 June 1998