D. H. Abbott

Micro‐ and macrogeographical genetic structure of colonies of naked mole‐rats Heterocephalus glaber

Patterns of genetic structure in eusocial naked mole‐rat populations were quantified within and among geographically distant populations using multilocus DNA fingerprinting and mitochondrial DNA (mtDNA) sequence analysis. Individuals within colonies were genetically almost monomorphic, sharing the same mtDNA control region haplotype and having coefficients of band sharing estimated from DNA fingerprints ranging from 0.93 to 0.99. Family analysis of a hybrid captive colony of naked mole‐rats with increased levels of genetic variability using multilocus DNA fingerprinting gave results consistent with Mendelian inheritance, and has revealed for the first time that multiple paternity can occur. In a survey of wild colonies from Ethiopia, Somalia and locations in northern and southern Kenya, we have examined mtDNA control region sequence variation in 42 individuals from 15 colonies, and together with multilocus DNA fingerprinting and mtDNA cytochrome‐b sequence analysis in selected individuals have shown that these populations show considerable genetic divergence. Most of the variance in sequence divergence was found to be between geographical locations (Φct= 0.68) and there was a significant correlation between sequence divergence and geographical separation of haplotypes. Six colonies from Mtito Andei in southern Kenya shared the same control region haplotype, suggesting a recent common maternal ancestor. In contrast, out of four colonies at Lerata in north Kenya, three haplotypes were identified, and phylogenetic analysis suggests that this area may be a zone where two distinct lineages are in close proximity. Genetic distances were maximal between Ethiopian and southern Kenyan populations at 5.8% for cytochrome‐b, and are approaching interspecific values seen between other Bathyergids.

Combined olfactory contact with the parent colony and direct contact with nonbreeding animals does not maintain suppression of ovulation in female naked mole-rats (Heterocephalus glaber)

The study investigated the role of odor cues from two naked mole-rat colonies, in conjunction with behavioral cues from nonbreeding colony members, in maintaining suppression of ovulation in subordinate female naked mole-rats isolated from the two parent colonies. Four high ranking nonbreeding female naked mole-rats were removed from their respective parent colonies and singly housed in separate burrow systems. For a 64-day period, the removed females were maintained in daily odor contact with their parent colony by daily rotating soiled bedding material between the parent colony and the burrow systems of removed females. In addition, subsets of nonbreeding animals from the respective parent colony were regularly moved into the burrow systems of removed females for 2-day periods during this 64-day period. Removed females were therefore in continual social contact with subsets of parent colony animals except for the breeding pair. All four removed females exhibited raised levels of urinary progesterone (< 2 ng/mg Cr) indicative of the onset of ovarian function within 3 days of being separated from the parent colony. Removed females exhibited a normal ovulatory cycle with levels of progesterone remaining elevated for 25-35 days (mean concentration of progesterone +/- SEM; 16.2 +/- 2 ng/mg Cr). Initiation of aggression and sexual behavior by removed females increased significantly when they were isolated from the parent colony. The results demonstrated that odor cues from the complete colony in conjunction with behavioral/tactile/vocal cues from the nonbreeding colony members were not the major cues maintaining reproductive suppression in nonbreeding female naked mole-rats. Instead, our results suggest that female reproductive suppression in naked mole-rats is caused by a dominance-related behavioral mechanism requiring direct contact with the breeding female.

Social dominance and the induction of infertility in subordinate female marmoset monkeys

The common marmoset monkey, Callithrixjacchus probably provides the best primate example of the social suppression of female reproduction. A single dominant female suppresses breeding in all female subordinates in her social group, mostly through suppression of their ovulatory cycles. To elucidate the behavioural and physiological mechanisms imposing this strict fertility on subordinate females, over 50 standardized laboratory groups of unrelated post-pubertal marmosets were formed, comprising two to four females and two to four males. Only six to eight groups were maintained at any one time. Quantitative behavioural observations showed clear intra-sexual hierarchies within each group, with a distinct dominant (Rank 1 ) male and female which formed a pair-bond and became the breeding animals. Subordinate females (Ranks 2 and below) exhibited little or no sexual behaviour, 75% became totally anovulatory and the remainder underwent infrequent and inadequate ovarian cycles. This reproductive suppression was readily reversed by removing females from their subordinate status. Impaired hypothalamic GnRH and pituitary LH secretion were implicated in the suppression of ovarian function. However, there was no evidence of elevated blood levels of cortisol or prolactin, or low body weight in subordinates. A combination ofbehavioural and pheromonal cues from dominant female marmosets were identified in the initiation and maintenance of subordinate infertility. Socially induced suppression of reproduction in colonies of naked mole-rats C.G. Faulkes, D.H. A b b o t t a n d T . E . S m i t h Institute of Zoology Zoological Society of London Regents Park London NWI 4RY, UK