| 1. |
- Jones, Owen R., et al.
(författare)
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Senescence rates are determined by ranking on the fast-slow life-history continuum
- 2008
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 11:7, s. 664-673
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Tidskriftsartikel (refereegranskat)abstract
- Comparative analyses of survival senescence by using life tables have identified generalizations including the observation that mammals senesce faster than similar-sized birds. These generalizations have been challenged because of limitations of life-table approaches and the growing appreciation that senescence is more than an increasing probability of death. Without using life tables, we examine senescence rates in annual individual fitness using 20 individual-based data sets of terrestrial vertebrates with contrasting life histories and body size. We find that senescence is widespread in the wild and equally likely to occur in survival and reproduction. Additionally, mammals senesce faster than birds because they have a faster life history for a given body size. By allowing us to disentangle the effects of two major fitness components our methods allow an assessment of the robustness of the prevalent life-table approach. Focusing on one aspect of life history - survival or recruitment - can provide reliable information on overall senescence.
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| 2. |
- Bonnet, Timothee, et al.
(författare)
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Genetic variance in fitness indicates rapid contemporary adaptive evolution in wild animals
- 2022
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 376:6596, s. 1012-1016
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Tidskriftsartikel (refereegranskat)abstract
- The rate of adaptive evolution, the contribution of selection to genetic changes that increase mean fitness, is determined by the additive genetic variance in individual relative fitness. To date, there are few robust estimates of this parameter for natural populations, and it is therefore unclear whether adaptive evolution can play a meaningful role in short-term population dynamics. We developed and applied quantitative genetic methods to long-term datasets from 19 wild bird and mammal populations and found that, while estimates vary between populations, additive genetic variance in relative fitness is often substantial and, on average, twice that of previous estimates. We show that these rates of contemporary adaptive evolution can affect population dynamics and hence that natural selection has the potential to partly mitigate effects of current environmental change.
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| 3. |
- Francioli, Yannick, et al.
(författare)
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Breeders are less active foragers than non-breeders in wild Damaraland mole-rats
- 2020
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Ingår i: Biology Letters. - : Royal Society. - 1744-9561 .- 1744-957X. ; 16:10
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Tidskriftsartikel (refereegranskat)abstract
- Eusocial societies are characterized by a clear division of labour between non-breeding workers and breeding queens, and queens often do not contribute to foraging, defence and other maintenance tasks. It has been suggested that the structure and organization of social mole-rat groups resembles that of eusocial insect societies. However, the division of labour has rarely been investigated in wild mole-rats, and it is unknown whether breeders show decreased foraging activity compared with non-breeding helpers in natural groups. Here, we show that, in wild Damaraland mole-rats (Fukomys damarensis), breeders show lower activity in foraging areas than non-breeding group members. Both breeders and non-breeders displayed variation in activity across the different seasons. Our results suggest that group living allows social mole-rat breeders to reduce their investment in energetically costly behaviour, or alternatively, that the high cost of reproduction in this species forces a behavioural trade-off against foraging investment.
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| 4. |
- Houslay, Thomas M., et al.
(författare)
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Benefits of cooperation in captive Damaraland mole-rats
- 2020
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Ingår i: Behavioral Ecology. - : Oxford University Press. - 1045-2249 .- 1465-7279. ; 31:3, s. 711-718
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Spong, Göran F., et al.
(författare)
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Factors affecting the reproductive success of dominant male meerkats
- 2008
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Ingår i: Molecular Ecology. - 0962-1083 .- 1365-294X. ; 17:9, s. 2287-2299
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Tidskriftsartikel (refereegranskat)abstract
- Identifying traits that affect the reproductive success of individuals is fundamental for our understanding of evolutionary processes. In cooperative breeders, a dominant male typically restricts mating access to the dominant female for extended periods, resulting in pronounced variation in reproductive success among males. This may result in strong selection for traits that increase the likelihood of dominance acquisition, dominance retention and reproductive rates while dominant. However, despite considerable research on reproductive skew, few studies have explored the factors that influence these three processes among males in cooperative species. Here we use genetic, behavioural and demographic data to investigate the factors affecting reproductive success in dominant male meerkats (Suricata suricatta). Our data show that dominant males sire the majority of all offspring surviving to 1 year. A male's likelihood of becoming dominant is strongly influenced by age, but not by weight. Tenure length and reproductive rate, both important components of dominant male reproductive success, are largely affected by group size and composition, rather than individual traits. Dominant males in large groups have longer tenures, but after this effect is controlled, male tenure length also correlates negatively to the number of adult females in the group. Male reproductive rate also declines as the number of intra- and extra-group competitors increases. As the time spent in the dominant position and reproductive rate while dominant explain > 80% of the total variance in reproductive success, group composition thus has major implications for male reproductive success.
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| 6. |
- Thorley, Jack, et al.
(författare)
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Damaraland mole-rats do not rely on helpers for reproduction or survival
- 2023
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Ingår i: Evolution Letters. - : Oxford University Press. - 2056-3744. ; 7:4, s. 203-215
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Tidskriftsartikel (refereegranskat)abstract
- In eusocial invertebrates and obligate cooperative breeders, successful reproduction is dependent on assistance from non-breeding group members. Although naked (Heterocephalus glaber) and Damaraland mole-rats (Fukomys damarensis) are often described as eusocial and their groups are suggested to resemble those of eusocial insects more closely than groups of any other vertebrate, the extent to which breeding individuals benefit from the assistance of non-breeding group members is unclear. Here we show that, in wild Damaraland mole-rats, prospective female breeders usually disperse and settle alone in new burrow systems where they show high survival rates and remain in good body condition-often for several years-before being joined by males. In contrast to many obligate cooperative vertebrates, pairs reproduced successfully without non-breeding helpers, and the breeding success of experimentally formed pairs was similar to that of larger, established groups. Though larger breeding groups recruited slightly more pups than smaller groups, adult survival was independent of group size and group size had mixed effects on the growth of non-breeders. Our results suggest that Damaraland mole-rats do not need groups to survive and that cooperative breeding in the species is not obligate as pairs can-and frequently do-reproduce without the assistance of helpers. While re-emphasizing the importance of ecological constraints on dispersal in social mole-rats, the mixed effects of group size in our study suggest that indirect benefits accrued through cooperative behavior may have played a less prominent role in the evolution of mole-rat group-living than previously thought. Lay Summary Social mole-rats are subterranean rodents that live in family groups where a single breeding female is responsible for the production of all pups. It has frequently been suggested that her non-breeding offspring act as helpers and increase the survival of all group members through cooperative foraging, which is thought to increase the rate at which tubers and other geophytes-the principal food of mole-rats-are found. Such helper effects are expected to generate positive associations between group size and reproduction, growth, and survival, but have rarely been looked for in wild populations. After monitoring a population of Damaraland mole-rats in the Southern Kalahari over 7 years, we found that the effect of non-breeders on the reproductive output of breeding females was modest: large groups recruited only slightly more offspring than smaller groups, and the experimental creation of breeding pairs showed that newly formed groups can start breeding immediately and reproduce at rates comparable to established groups. Effects of group size on individual growth rates and on individual survival were also limited, with solitary females in particular-females who have dispersed from their natal group and settled alone-showing high survival rates that approached that of breeding females. Taken together, our results suggests that the extent to which breeding females rely on non-breeders as helpers in mole-rat societies may be less pronounced than previously thought. Helper effects appear relatively weak and the principal reason that offspring delay dispersal is likely because of the strong constraints on dispersal in this species.
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| 7. |
- Thorley, Jack, et al.
(författare)
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No task specialization among helpers in Damaraland mole-rats
- 2018
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Ingår i: Animal Behaviour. - : Elsevier. - 0003-3472 .- 1095-8282. ; 143, s. 9-24
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Tidskriftsartikel (refereegranskat)abstract
- The specialization of individuals in specific behavioural tasks is often attributed either to irreversible differences in development, which generate functionally divergent cooperative phenotypes, or to agerelated changes in the relative frequency with which individuals perform different cooperative activities; both of which are common in many insect caste systems. However, contrasts in cooperative behaviour can take other forms and, to date, few studies of cooperative behaviour in vertebrates have explored the effects of age, adult phenotype and early development on individual differences in cooperative behaviour in sufficient detail to discriminate between these alternatives. Here, we used multinomial models to quantify the extent of behavioural specialization within nonreproductive Damaraland mole-rats, Fukomys damarensis, at different ages. We showed that, although there were large differences between individuals in their contribution to cooperative activities, there was no evidence of individual specialization in cooperative activities that resembled the differences found in insect societies with distinct castes where individual contributions to different activities are negatively related to each other. Instead, individual differences in helping behaviour appeared to be the result of age-related changes in the extent to which individuals committed to all forms of helping. A similar pattern is observed in cooperatively breeding meerkats, Suricata suricatta, and there is no unequivocal evidence of caste differentiation in any cooperative vertebrate. The multinomial models we employed offer a powerful heuristic tool to explore task specialization and developmental divergence across social taxa and provide an analytical approach that may be useful in exploring the distribution of different forms of helping behaviour in other cooperative species. (C) 2018 The Authors. Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.
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| 8. |
- Thorley, Jack, et al.
(författare)
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Reproduction triggers adaptive increases in body size in female mole-rats
- 2018
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society Publishing. - 0962-8452 .- 1471-2954. ; 285:1880
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Tidskriftsartikel (refereegranskat)abstract
- 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 (Fukomys damarensis), 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.
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| 9. |
- Vullioud, Philippe, et al.
(författare)
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Increases in glucocorticoids are sufficient but not necessary to increase cooperative burrowing in Damaraland mole-rats
- 2021
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Ingår i: Hormones and Behavior. - : Elsevier. - 0018-506X .- 1095-6867. ; 135
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Tidskriftsartikel (refereegranskat)abstract
- Despite widespread interest in the evolution of cooperative behaviour, the physiological mechanisms shaping their expression remain elusive. We tested the hypothesis that glucocorticoid (GC) hormones affect cooperative behaviour using captive Damaraland mole-rats (Fukomys damarensis), a cooperatively breeding mammal. Within groups, individuals routinely contribute to public goods that include foraging tunnels, which provide all group members access to the tubers of desert plants they feed on, communal food stores and nests. We found that experimental increases in glucocorticoid concentration (GCc) in non-breeding female helpers led them to be active for longer and to burrow more while active, raising their daily contributions to burrowing, but not food carrying or nest building. However, experimentally induced increases in burrowing did not lead to elevated GCc in helpers of both sexes. These results suggest that heightened GCc may stimulate some cooperative behaviours that are energetically demanding (a characteristic shared by many types of cooperative activities across species) but that the cooperative behaviours affected by GCc can also be regulated by other mechanisms.
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| 10. |
- Zöttl, Markus, et al.
(författare)
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Allo-parental care in Damaraland mole-rats is female biased and age dependent, though independent of testosterone levels
- 2018
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Ingår i: Physiology and Behavior. - : Elsevier. - 0031-9384 .- 1873-507X. ; 193, s. 149-153
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Tidskriftsartikel (refereegranskat)abstract
- In Damaraland mole-rats (Fukomys damal-ensis), non-breeding subordinates contribute to the care of offspring born to the breeding pair in their group by carrying and retrieving young to the nest. In social mole-rats and some cooperative breeders, dominant females show unusually high testosterone levels and it has been suggested that high testosterone levels may increase reproductive and aggressive behavior and reduce investment in allo-parental and parental care, generating age and state-dependent variation in behavior. Here we show that, in Damaraland mole-rats, allo-parental care in males and females is unaffected by experimental increases in testosterone levels. Pup carrying decreases with age of the non-breeding helper while the change in social status from non-breeder to breeder has contrasting effects in the two sexes. Female breeders were more likely than female non-breeders to carry pups but male breeders were less likely to carry pups than male non-breeders, increasing the sex bias in parental care compared to allo-parental care. Our results indicate that testosterone is unlikely to be an important regulator of allo-parental care in mole-rats.
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