Reproductive Biology of a Tropical, Non-Hibernating Ground Squirrel

Waterman, Jane M.

doi:10.2307/1382715

Cited by 55 publications

(78 citation statements)

References 64 publications

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“…Female Cape ground squirrels reach sexual maturity from 8 to 10 months (Waterman, 1996(Waterman, , 2002, when they are expected to attain a mass of 540-580 g. Our study, however, suggests that the mean mass of non-breeding is around 585 g and we therefore conclude that many of the non-breeding females in our study, while old enough to reproduce, did not do so. From these observations, it is easy to conclude that these non-breeders are reproductively repressed by either behavioural or physiological means (see Waterman, 2002).…”

Section: Discussioncontrasting

confidence: 71%

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Pituitary luteinizing hormone responses to single doses of exogenous GnRH in female social Cape ground squirrels exhibiting low reproductive skew

Jackson¹,

Waterman²,

Bennett³

2007

Journal of Zoology

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The Cape ground squirrel Xerus inauris is unusual among social mammals as it exhibits a low reproductive skew, being a facultative plural breeder with not all females breeding within a group. We investigated pituitary function to assess whether there was reproductive inhibition at the level of the pituitary and potentially the hypothalamus in breeding and non-breeding female Cape ground squirrels. We did so during the summer and winter periods by measuring luteinizing hormone (LH) responses to single doses of 2 g exogenous gonadotropin-releasing hormone (GnRH) and physiological saline openUP administered to 42 females from 11 colonies. Basal LH concentrations of females increased in response to the GnRH challenge. Basal plasma LH concentrations were greater during winter, when most oestrus events are observed. However, we found no differences in plasma LH concentrations between breeding and non-breeding females.We showed that the anterior pituitary of non-breeding female ground squirrels is no less sensitive to exogenously administered GnRH than that of breeding females. We therefore concluded that the pituitary is no more active in breeding than non-breeding females. The lack of differentiation in response to GnRH suggests that either non-breeding females have ovaries that are less sensitive to LH or that they refrain from sexual activity with males through an alternative mechanism of self-restraint.

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Section: Discussioncontrasting

confidence: 71%

“…The nipples of breeding females swell during the first gestation and remain permanently swollen thereafter (Waterman, 1995). During lactation, these nipples increase to almost 2 cm in length (Waterman, 1996). Non-breeding females were characterized by their rudimentary nipples (<0.5 cm long) and small vulvas.…”

Section: Assessment Of Reproductive Statusmentioning

confidence: 99%

Pituitary luteinizing hormone responses to single doses of exogenous GnRH in female social Cape ground squirrels exhibiting low reproductive skew

Jackson¹,

Waterman²,

Bennett³

2007

Journal of Zoology

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“…Given that female Cape ground squirrels mate with multiple males (Waterman, 1998), a large relative testes size is expected, as males should invest more in testicular tissue to increase the number of sperm per ejaculate. However, unlike other rodents where larger testes are also correlated with multiply sired litters (Ramm et al, 2005), Cape ground squirrels, with an average litter size of 1.6, are less likely to have multiply sired litters (Waterman, 1996). A small litter size does not, however, preclude a high level of sperm competition; in fact, it may encourage greater investment in competitive ejaculates due to the low paternity returns expected from each female.…”

Section: Discussionmentioning

confidence: 93%

“…While females may exert some level of mate choice by retreating underground with specific males, older, more dominant males typically obtain the first copulation of a female's oestrous (Waterman, 1998). The dominance hierarchy of males, however, is unrelated to external testes size or body size (Waterman, 1998): males have very obviously large external testes, about 20% of the head-body length (Waterman, 1998), and show no seasonality in external testicle size (Waterman, 1996).…”

Section: Introductionmentioning

confidence: 99%

Structure and allometry of genitalia in males and females of a social African ground squirrel with high polygynandry

et al. 2008

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The few studies that have looked at genital allometry in mammals have typically shown a positively allometric relationship with body size and high coefficients of variation. Cryptic female choice, sexual conflict or sperm competition are mechanisms underlying genital evolution and as these are not mutually exclusive, they are often difficult to disentangle. In addition, these mechanisms are affected by both male and female social structure and/or mating strategies and, as such, pre-and post-copulatory behaviours have been shown to alter selection on genitalia. We examined genital traits and allometry in a polygynandrous and social ground squirrel Xerus inauris. We found that male testes are positively allometric and account for 1.5% of their body weight, one of the highest percentages known for sciurids. The penis, at 42.4% of head/body length, was isometric while the female reproductive tract, 22.4% head/body length, demonstrated no such relationship. Based on the allometric relationships of both males and females presented here, in conjunction with high levels of competition for females and lack of male aggression and territoriality, we suggest that sperm competition is the most likely mechanism for the evolution of the extremely large genitalia in this species.

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“…One report of females bein g larger than males was based on 2 males and 9 females (Raut enbach 1982) . Average len gth (in mm) of selected external measurements for males and females, respectivel y, are: total length , 452-476, 435-446 ;length of head and body, 243-282, 235-248;length of tail , 194-2II , 196-207;length of hind foot, 62-68, 64-66;length of ear, 9-12, 9-13 (Berna rd and Nurton 1993;Herzig-Straschil I 9 78;Lynch 1983;Smithers 1971 ;Waterman 1996).…”

Section: General Characters Xerus Inauris Is Covered Withmentioning

confidence: 99%