| 1. |
- Bensch, Hanna, et al.
(författare)
-
Within-group sex ratios predict growth of social mole-rats
- 2024
-
Ingår i: Journal of Zoology. - : John Wiley & Sons. - 0952-8369 .- 1469-7998.
-
Tidskriftsartikel (refereegranskat)abstract
- Groups of wild animals can vary considerably in their composition, including in the proportion of group members which are male or female, the within-group sex ratio. Variation in within-group sex ratios can arise from active adjustment of litter sex ratios by mothers, from sex differences in mortality, dispersal and immigration, or from stochastic variation in recruitment. Irrespective of its origins, variation in the within-group sex ratio can have consequences for within-group competition and can affect individual life histories throughout development. In this paper, we explore which processes may generate variation in within-group sex ratios in wild Damaraland mole-rats (Fukomys damarensis), a singular cooperative breeder, and we investigate whether within-group sex ratios predict the growth, body condition and philopatry of individuals. We show that although the population-level sex ratio is balanced, skewed within-group sex ratios are common, particularly among small groups. Our data suggests that stochastic variation in the sex of recruits explains natural variation in the sex ratio of wild groups. Non-breeding individuals in groups with a sex ratio biased towards their own sex grow more slowly than individuals in groups biased towards the opposite sex, suggesting that intra-sexual competition may decrease growth rates. We suggest that the costs of competition may contribute to the large variation in growth observed in social mole-rat groups.
|
|
| 2. |
- Finn, Kyle T., et al.
(författare)
-
Subterranean Life-Style Does Not Limit Long Distance Dispersal in African Mole-Rats
- 2022
-
Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media S.A.. - 2296-701X. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Dispersal from the natal site to breeding sites is a crucial phase in the life history of animals and can have profound effects on the reproductive ecology and the structure of animal societies. However, few studies have assessed dispersal dynamics in subterranean mammals and it is unknown whether dispersal distances are constrained by living underground. Here we show, in social, subterranean Damaraland mole-rats (Fukomys damarensis), that a subterranean lifestyle does not preclude long distance dispersal and that both sexes are capable of successfully dispersing long distances (>4 km). Body condition did not predict dispersal distance, but dispersers from larger groups traveled farther than individuals from smaller groups. Subsequently we show in a phylogenetically controlled comparative analysis of dispersal distances in subterranean and surface-dwelling rodents that living underground does not constrain dispersal distances and that dispersal capacity is mainly a consequence of body size in both lifestyles.
|
|
| 3. |
- Francioli, Yannick, et al.
(författare)
-
Breeders are less active foragers than non-breeders in wild Damaraland mole-rats
- 2020
-
Ingår i: Biology Letters. - : Royal Society. - 1744-9561 .- 1744-957X. ; 16:10
-
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.
|
|
| 4. |
- Stervander, Martin, et al.
(författare)
-
High MHC gene copy number maintains diversity despite homozygosity in a Critically Endangered single-island endemic bird, but no evidence of MHC-based mate choice
- 2020
-
Ingår i: Molecular Ecology. - : John Wiley & Sons. - 0962-1083 .- 1365-294X. ; 29:19, s. 3578-3592
-
Tidskriftsartikel (refereegranskat)abstract
- Small population sizes can, over time, put species at risk due to the loss of genetic variation and the deleterious effects of inbreeding. Losing diversity in the major histocompatibility complex (MHC) could be particularly harmful, given its key role in the immune system. Here, we assess MHC class I (MHC-I) diversity and its effects on mate choice and survival in the Critically Endangered Raso larkAlauda razae, a species restricted to the 7 km(2)islet of Raso, Cape Verde, since similar to 1460, whose population size has dropped as low as 20 pairs. Exhaustively genotyping 122 individuals, we find no effect of MHC-I genotype/diversity on mate choice or survival. However, we demonstrate that MHC-I diversity has been maintained through extreme bottlenecks by retention of a high number of gene copies (at least 14), aided by cosegregation of multiple haplotypes comprising 2-8 linked MHC-I loci. Within-locus homozygosity is high, contributing to low population-wide diversity. Conversely, each individual had comparably many alleles, 6-16 (average 11), and the large and divergent haplotypes occur at high frequency in the population, resulting in high within-individual MHC-I diversity. This functional immune gene diversity will be of critical importance for this highly threatened species' adaptive potential.
|
|
| 5. |
- Thorley, Jack, et al.
(författare)
-
Damaraland mole-rats do not rely on helpers for reproduction or survival
- 2023
-
Ingår i: Evolution Letters. - : Oxford University Press. - 2056-3744. ; 7:4, s. 203-215
-
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.
|
|
| 6. |
- Thorley, Jack, et al.
(författare)
-
No task specialization among helpers in Damaraland mole-rats
- 2018
-
Ingår i: Animal Behaviour. - : Elsevier. - 0003-3472 .- 1095-8282. ; 143, s. 9-24
-
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.
|
|
| 7. |
- Thorley, Jack, et al.
(författare)
-
Reproduction triggers adaptive increases in body size in female mole-rats
- 2018
-
Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society Publishing. - 0962-8452 .- 1471-2954. ; 285:1880
-
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.
|
|
| 8. |
- Zöttl, Markus, et al.
(författare)
-
Capture Order Across Social Bathyergids Indicates Similarities in Division of Labour and Spatial Organisation
- 2022
-
Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media S.A.. - 2296-701X. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- The social mole-rats of the family Bathyergidae show elaborate social organisation that may include division of labour between breeders and non-breeders as well as across non-breeders within their groups. However, comparative behavioural data across the taxa are rare and contrasts and similarities between species are poorly understood. Field studies of social bathyergids usually involve capturing all group members until the entire group is captured. Because each animal is only captured once and traps are typically placed in close proximity to active foraging areas, the order in which animals are captured provides an indication of the foraging activity of different individuals and of the spatial organisation of the group within the burrow system. Here, we compare the association of capture order with breeding status, sex, and body mass in four species and subspecies of social bathyergids, which vary in group size and represent all three social genera within the family Bathyergidae. We show that in naked and Damaraland mole-rats (Heterocephalus glaber and Fukomys damarensis), male and female breeders are captured later than non-breeders, whereas in two different subspecies of the genus Cryptomys only female breeders are captured later than non-breeders. The effect sizes vary largely and are 10 times larger in naked mole-rats as compared to Fukomys and 3-4 times larger than in Cryptomys. Among non-breeders, sex effects are notably absent in all species and body mass predicted capture order in both naked and Damaraland mole-rats. In naked mole-rats, larger non-breeders were captured earlier than smaller ones, whereas in Damaraland mole-rats intermediate-sized non-breeders were captured first. Our data suggest that there are similarities in behavioural structure and spatial organisation across all social bathyergid species, though the most pronounced differences within groups are found in naked mole-rats.
|
|
