La conversión infinita del escritor

4.4 DISCUSSION: FEMALES

The results from this study showed clear differences in the structure and development o f the reproductive tra c t and ovaries between breeding and non-breeding female naked mole-rats. In breeders, both the absolute and relative to body mass size dimensions measured were significantly greater than in non-breeders, as illustrated in Plate 4.1. The ovaries and reproductive tra c t o f non-breeding females had an underdeveloped appearance: both ovaries and uteri were small and lacked a well developed vascular supply (previously reported by Kayanja & Jarvis, 1971). This is evident in Plate 4.1, particularly in tra c t 'c1. The gross appearance and size o f the reproductive tra c t o f non-breeding females suggests that none o f the 59 captive and wild-caught non-breeders examined had previously bred, and th at the presumption o f non-breeding status based on morphological differences was correct.

Histological observation o f the ovary provides further insight into the nature o f the block to reproduction in non-breeding females. In contrast to breeders, the ovaries o f non-breeders completely lacked any form o f luteal tissue, including post-ovulatory corpora lutea and accessory corpora lutea. In addition, follicular development was limited and did not go beyond the secondary follicle stage, except in one wild-caught female (4.11, Plate 4.7). These observations suggest that non-breeding females do not reproduce because they do not ovulate.

The presence o f corpora lutea in female 18, a test animal in a bedding transfer experiment (see Chapter 8), confirms that this female had undergone ovulatory cycles (examination o f serial sections did not reveal any unovulated oocytes within this luteal tissue), despite being removed from her colony and paired with a male, but kept in odour contact with the parent colony. Although urinary progesterone profiles o f this female (illustrated in Chapter 8, Figure 8.1) had shown that ovarian cycles had ceased due to weight loss and illness, luteal tissue had persisted in the ovary, although it was not apparently excreting progesterone in concentrations similar to those found during the normal luteal phase. The persistence o f luteal tissue in the ovaries o f breeding females provides further validity to the hypothesis that non-breeding females fa il to ovulate, i.e. it would be unlikely to not see corpora lutea in a t least some non-breeders had they been undergoing ovarian cycles. This is in keeping with the endocrine studies reported in Chapter 5, which have shown that non-breeding females have urinary and

plasma progesterone concentrations below the sensitivity limit o f the assay, suggesting th a t ovulation and subsequent corpus iuteum form ation was not occurring.

It is interesting th a t accessory corpora lutea, arising from the luteinisation o f unovulated fo llicles, are present in the ovaries o f breeding female naked m ole-rats. These occur during pregnancy, exemplified by female 501 (Plate 4 .3 ), which died 36 h post-partum , and in non-pregnant animals (Kayanja & Jarvis, 1971). These structures have been reported to be present in other hystricomorph rodents, e.g., chinchilla, Chinchilla lanigert Canadian porcupine, Ereihizon dorsatum, and mountain viscacha, Lagidium peruanum (Weir & Rowlands, 1974). Among other members o f the fam ily Bathyergidae, the A frican m ole-rats, accessory corpora lutea have been reported in the ovaries o f both reproductive, and in co n trast to the naked m ole-rat, also in non- reproductive females o f the two other socially living species, Cryptomys h. hottentotus and C. h. damarensis (Bennett, 1988, 1989). The ovaries o f the solitary Bathyergid, Georychus capensis, also contain accessory corpora lutea outside the breeding season (Bennett, 1988). The physiological significance o f these structures in non-reproductive animals is not known, but in breeding individuals, accessory corpora lutea may enhance progesterone secretion fo r the maintenance o f pregnancy during the comparatively long gestational periods o f hystricomorphs (Tam, 1974; see Chapter 5).

4 .5 RESULTS: MALES 4.5.1 ANATOMY

The absolute and relative to body mass reproductive tr a c t masses (testes, epididymus and vas deferens) fo r captive breeding and non-breeding males, and wild-caught males o f unknown status are listed in Table 4 .3 below.

1 MALE STATUS TOTAL MASS OF REPRODUCTIVE TRACT (mg) 1 TOTAL MASS OF 1 1 TRACT/BODY 1 1 MASS 1 1 (mg/g) 1 1 CAPTIVE 79.0 4 14.7tt 1 2.0 4 0 .2 * # 1 1 BREEDER c H 1 n=4 1 1 CAPTIVE 34.0 4 2.9 1 1.2 4 0.1 1 1 NON-BREEDER n=6 I n=6 1 1 WILD 33.9 4 2.2 1 1.5 4 0.3 1 1 CAUGHT n=52 1 n=52 1 1 1 1 1

TABLE 4 .3 - Mean 1 sem to ta l and relative to body mass reproductive tr a c t mass expressed per gram body mass in n captive breeding, non-breeding and wild-caught male naked m ole-rats. tt= P < 0.01 vs captive non-breeding and wild-caught status, to ta l mass. * * = P < 0.01 vs captive non-breeding status, relative mass.

Relative to body mass, breeding males had significantly higher to ta l reproductive tr a c t mass (P < 0.01, t= 3.70, D.F.= 8), compared to captive non-breeding males. The absolute masses o f reproductive tr a c ts were also significantly d iffe re n t between captive breeding and captive non-breeding males (P < 0.01, t= 3.59, D .F.= 8), and between captive breeding and wild- caught males (P < 0.01, t= 3.03, D.F.= 54). A t the time o f capture, it was not known whether or not the wild-caught males included any breeders. However, the mass o f the reproductive tr a c ts o f wild-caught males resemble those o f captive non-breeders, but not o f captive breeders. I t was th erefo re

likely th a t the reproductive tr a c ts o f the wild-caught males were all from non-breeders.