Alloparental brood care, where individuals help raising the offspring of others, is generally believed to be favoured by high degrees of relatedness between helpers and recipients. Here we show that in cooperatively breeding cichlids, unrelated subordinate females provide more alloparental care than related ones when kinship between dominant and subordinate group members is experimentally manipulated. In addition, unrelated helpers increased alloparental care after we simulated egg cannibalism by helpers, an effect not shown by related helpers. By supporting predictions of pay-to-stay theory, these results suggest that in Neolamprologus pulcher, reciprocal commodity trading is important for the decision of subordinates to invest in care of the dominants' offspring.

In cooperative breeding systems, dominant breeders sometimes tolerate unrelated individuals even if they inflict costs on the dominants. According to the 'pay-to-stay' hypothesis, (i) subordinates can outweigh these costs by providing help and (ii) dominants should be able to enforce help by punishing subordinates that provide insufficient help. This requires that dominants can monitor helping and can recognize group members individually. In a field experiment, we tested whether cooperatively breeding cichlid Neolamprologus pulcher subordinates increase their help after a forced 'idle' period, how other group members respond to a previously idle helper, and how helper behaviour and group responses depend on group size. Previously idle helpers increased their submissiveness and received more aggression than control helpers, suggesting that punishment occurred to enforce help. Subordinates in small groups increased their help more than those in large groups, despite receiving less aggression. When subordinates were temporarily removed, dominants in small groups were more likely to evict returning subordinates. Our results suggest that only in small groups do helpers face a latent threat of punishment by breeders as predicted by the pay-to-stay hypothesis. In large groups, cognitive constraints may prevent breeders from tracking the behaviour of a large number of helpers.

In many cooperative breeders, the contributions of helpers to cooperative activities change with age, resulting in age-related polyethisms. In contrast, some studies of social mole rats (including naked mole rats, Heterocephalus glaber, and Damaraland mole rats, Fukomys damarensis) suggest that individual differences in cooperative behavior are the result of divergent developmental pathways, leading to discrete and permanent functional categories of helpers that resemble the caste systems found in eusocial insects. Here we show that, in Damaraland mole rats, individual contributions to cooperative behavior increase with age and are higher in fast-growing individuals. Individual contributions to different cooperative tasks are intercorrelated and repeatability of cooperative behavior is similar to that found in other cooperatively breeding vertebrates. Our data provide no evidence that nonreproductive individuals show divergent developmental pathways or specialize in particular tasks. Instead of representing a caste system, variation in the behavior of nonreproductive individuals in Damaraland mole rats closely resembles that found in other cooperatively breeding mammals and appears to be a consequence of age-related polyethism.division of labor | eusociality | caste | cooperative breeding | social mole rats I n cooperatively breeding vertebrates and primitively eusocial insects, subordinate group members frequently vary widely in their investment in cooperative tasks. These differences are often consequences of state-dependent changes in fitness costs and benefits, which vary with age, growth, and sex (1-6), and result in age-and sex-related polyethisms where behavior varies in relation to opportunities to breed. In cooperatively breeding meerkats (Suricata suricatta) for example, fast growing helpers contribute more to overall cooperative behavior; supplementary feeding increases help; and subordinates do not specialize in certain tasks (3, 4, 7). Similar patterns are widespread among other cooperative breeders from diverse taxa [birds (8), mammals (9), fish (10, 11), and primitively eusocial insects (5, 6)].It has been suggested that naked mole rats (Heterocephalus glaber) and Damaraland mole rats (Fukomys damarensis) are an exception to this pattern (12)(13)(14). In these species, the main cooperative task performed by nonbreeding helpers (building a large network of foraging tunnels) is primarily carried out by small individuals of both sexes (12,(14)(15)(16)(17) and it has been argued previously that this may be the result of a caste system, similar to those found in some eusocial insect species. Some studies suggested that in mole rats, specialized, smaller workers conduct most of the energetically demanding burrowing and remain in this state for their entire life, whereas larger workers contribute little to cooperative burrowing but specialize in other cooperative tasks, including nest building, alloparental care, or colony defense (12,14). Others have argued that it is premature to assume that naked mole...

Invasive alien parasites and pathogens are a growing threat to biodiversity worldwide, which can contribute to the extinction of endemic species. On the Galápagos Islands, the invasive parasitic fly Philornis downsi poses a major threat to the endemic avifauna. Here, we investigated the influence of this parasite on the breeding success of two Darwin's finch species, the warbler finch (Certhidea olivacea) and the sympatric small tree finch (Camarhynchus parvulus), on Santa Cruz Island in 2010 and 2012. While the population of the small tree finch appeared to be stable, the warbler finch has experienced a dramatic decline in population size on Santa Cruz Island since 1997. We aimed to identify whether warbler finches are particularly vulnerable during different stages of the breeding cycle. Contrary to our prediction, breeding success was lower in the small tree finch than in the warbler finch. In both species P. downsi had a strong negative impact on breeding success and our data suggest that heavy rain events also lowered the fledging success. On the one hand parents might be less efficient in compensating their chicks' energy loss due to parasitism as they might be less efficient in foraging on days of heavy rain. On the other hand, intense rainfalls might lead to increased humidity and more rapid cooling of the nests. In the case of the warbler finch we found that the control of invasive plant species with herbicides had a significant additive negative impact on the breeding success. It is very likely that the availability of insects (i.e. food abundance)is lower in such controlled areas, as herbicide usage led to the removal of the entire understory. Predation seems to be a minor factor in brood loss.

Dispersal behaviour in cooperatively breeding mammals often differs between the sexes, which can affect how individuals of both sexes compete for breeding opportunities. However, it is largely unknown how the males and females in social mole‐rats differ in frequency, timing and social context of dispersal. Here we show, in Damaraland mole‐rats (Fukomys damarensis), that rainfall increases dispersal probabilities in both sexes. Dispersal is male biased with males dispersing earlier and more frequently in dispersal coalitions than females. Most non‐reproductive individuals disperse from the natal groups before reproducing. Territory inheritance is rare, but when it occurs, female non‐breeders inherit the breeding position from the precious breeding female. After dispersing from the natal group, males are more likely than females to join other established groups and to replace the resident breeder. Our study suggests that differences in dispersal strategy may generate contrasts in intra‐sexual competition, where male breeders are more often challenged by competitors from outside the group and female breeders may face higher competition from individuals within the group.

Socio-demographic factors, such as group size, and their effect on predation vulnerability, have, in addition to intrinsic factors, dominated as explanations when attempting to understand animal vigilance behaviour. It is generally assumed that animals evaluate these external factors visually, however many socially foraging species adopt a foraging technique that directly compromises the visual system. In these instances, such species may instead rely more on the acoustical medium to assess their relative risk and guide their subsequent anti-predator behaviour. We addressed this question in the socially foraging meerkat (Suricata suricatta). Meerkats forage with their head down, but at the same time frequently produce close calls ("Foraging" close calls). Close calls are also produced just after an individual has briefly scanned the surrounding environment for predators ("Guarding" close calls). Here, we firstly show that these Guarding and Foraging close call variants are in fact acoustically distinct and secondly subjects are less vigilant (in terms of frequency and time) when exposed to Guarding close call playbacks than when they hear Foraging close calls. We argue that this is the first evidence for socially foraging animals using the information encoded within calls, the main adaptive function of which is unrelated to immediate predator encounters, to coordinate their vigilance behaviour. In addition these results provide new insights into the potential cognitive mechanisms underlying anti-predator behaviour and suggest meerkats may be capable of signalling to group members the "absence" of predatory threat. If we are to fully understand the complexities underlying the coordination of animal anti-predator behaviour we encourage future studies to take these additional auditory and cognitive dimensions into account. in addition to intrinsic factors, dominated as explanations when attempting to understand animal 25 vigilance behaviour. It is generally assumed that animals evaluate these external factors visually, 26 however many socially foraging species adopt a foraging technique that directly compromises the 27 visual system. In these instances, such species may instead rely more on the acoustical medium to 28 assess their relative risk and guide their subsequent anti-predator behaviour. We addressed this 29 question in the socially foraging meerkat (Suricata suricatta). Meerkats forage with their head 30 down, but at the same time frequently produce close calls ("Foraging" close calls). Close calls are 31 also produced just after an individual has briefly scanned the surrounding environment for 32 predators ("Guarding" close calls). Here, we firstly show that these Guarding and Foraging close 33 call variants are in fact acoustically distinct and secondly subjects are less vigilant (in terms of 34 frequency and time) when exposed to Guarding close call playbacks than when they hear 35Foraging close calls. We argue that this is the first evidence for socially foraging animals using 36 the informat...

Although the social mole-rats are commonly classified as eusocial breeders on the grounds that groups include a single breeding female (the “queen”) and a number of nonbreeding individuals (“helpers”) of both sexes, alloparental care is not highly developed in these species and there is no direct evidence that the presence or number of nonbreeders is associated with reductions in the workload of the “queen.” An alternative interpretation of mole-rat groups is that the social mole-rats are cooperative foragers rather than cooperative or eusocial breeders. Here, in captive colonies of Damaraland mole-rats (Fukomys damarensis), we provide the first evidence that increases in the number of nonbreeding subordinates in mole-rat groups are associated with reductions in the workload of “queens” and with increases in their fecundity.

In social mole-rats, breeding females are larger and more elongated than non-breeding female helpers. This status-related morphological divergence is thought to arise from modifications of skeletal growth following the death or removal of the previous breeder and the transition of their successors from a non-breeding to a breeding role. However, it is not clear what changes in growth are involved, whether they are stimulated by the relaxation of reproductive suppression or by changes in breeding status, or whether they are associated with fecundity increases. Here, we show that, in captive Damaraland mole-rats (), where breeding was experimentally controlled in age-matched siblings, individuals changed in size and shape through a lengthening of the lumbar vertebrae when they began breeding. This skeletal remodelling results from changes in breeding status because (i) females removed from a group setting and placed solitarily showed no increases in growth and (ii) females dispersing from natural groups that have not yet bred do not differ in size and shape from helpers in established groups. Growth patterns consequently resemble other social vertebrates where contrasts in size and shape follow the acquisition of the breeding role. Our results also suggest that the increases in female body size provide fecundity benefits. Similar forms of socially responsive growth might be more prevalent in vertebrates than is currently recognized, but the extent to which this is the case, and the implications for the structuring of mammalian dominance hierarchies, are as yet poorly understood.