Failure of the Estrous Cycle and Spermatogenesis to Respond to Day Length in a Subtropical African Rodent, the Pouched Mouse (Saccostomus Campestris)1

Abstract

Little is known about the role of photoperiod in the control of reproduction in mammals from the tropics in general and, in particular, from the Afrotropics. The present study examined the reproductive photosensitivity of the pouched mouse (Saccostomus campestris: Cricetidae), a small, seasonally breeding rodent that occurs from about 12 degrees S to 33 degrees S in Africa. Groups of 10 laboratory-bred male pouched mice were exposed to either long-day (16L:8D) or short-day (8L:16D) conditions for 14 wk, after which they were killed and the spermatogenic activity of the testes was assessed histologically. A group of 10 adult, multiparous females were exposed to long-day conditions for 3 mo, after which the lengths of five consecutive estrous cycles were measured. Thereafter, day length was reduced to 10L:14D, and after 16 days acclimation, the lengths of five estrous cycles were measured. Finally, day length was reduced to 8L:16D, and after 33 days, the lengths of five estrous cycles were measured. Day length had no influence on body size, testis size, or the histology of the testis, and all specimens were actively producing spermatozoa. The length of the estrous cycle (4.0 +/- 0.3 days under long-day conditions) did not change significantly with the decrease in photoperiod. In a third experiment, 14 multiparous and six nulliparous females that had been maintained under short-day conditions for 33 days were mated and successfully reared litters.(ABSTRACT TRUNCATED AT 250 WORDS)

Social, but Not Photoperiodic, Influences on Reproductive Function in Male Peromyscus aztecus 1

“…Previous research has demonstrated that photoperiodic responsiveness n-I 387 --e decreases with decreasing latitude (reviewed in [3]). Generally, rodent species inhabiting low latitudes (i.e., below 10°N) stop responding to day length as a reproductive cue, whereas populations of high-latitude animals (i.e., above 10°N) display varying degrees of photoperiodic responsiveness [23]. The present results add further support to this pattern.…”

“…In many rodent species, seasonal patterns in reproduction may be entrained by photoperiod; short days signal the presence of winter and cause gonadal regression, while long days indicate spring and summer and stimulate gonadal recrudescence [3]. Alternatively, reproduction may be the result of an opportunistic strategy according to which breeding occurs only in the presence of an optimal climate and abundant food regardless of day length [23]. Previous research has demonstrated that photoperiodic responsiveness n-I 387 --e decreases with decreasing latitude (reviewed in [3]).…”

Physiological Constraints and Latitudinal Breeding Season in the Canidae

“…Local adjustments in reproductive seasonality near the equator have been well documented in birds (e.g., red crossbills, spotted antbirds, and stonechats) where long-term cues (tropical photoperiod) are used as predictors of the rainy season and short-term cues such as food availability, or rainfall itself, are used to fine-tune reproductive activities (Baker 1938;Gwinner and Scheuerlein 1999;Hau et al 2000;Wikelski et al 2000;Hau 2001). In contrast, the mechanisms of reproductive control in tropical mammals have been rarely studied, but there is some evidence that concentrations of plant secondary compounds may entrain seasonal rhythms (e.g., gerbils, Gerbillus hardwoodi; Alibhai 1986), food availability fine-tunes reproduction (e.g., pouched mouse, Saccostomus campestris; Bernard and Hall 1995), and light intensity acts as a seasonal zeitgeber (e.g., ground squirrels; Davis 1991).…”

Gender differences in the inhibitory effects of a reduction in ambient temperature and a reduction in food quantity on reproduction in the Southern African rodent, Rhabdomys pumilio

“…For each male, 100 randomly selected sections through seminiferous tubules from at least two sections through each testis were examined and classified as spermatogenically inactive (tubule lined by spermatogonia and Sertoli cells only), early spermatogenesis (seminiferous epithelium of spermatogonia and spermatocytes) or late spermatogenesis (spermiogenesis occurring with spermatozoa in the lumen of the tubule). An individual was placed into a specific category if > 70% of the tubules were in a particular condition (Bernard and Hall, 1995). Twenty sections through the cauda epididymides were examined and each animal was given a qualitative score depending on the amount of spermatozoa present in the sections (0: no spermatozoa present; 3: cauda epididymides more than three-quarters full of spermatozoa).…”

“…Therefore, the timing of rodent reproduction is usually shaped by complex interactions between a range of environmental, physiological and social factors (Harvey and Zammuto, 1985;Partridge and Harvey, 1985;Bronson, 1989;Read and Harvey, 1989;Promislow and Harvey, 1990;Bronson and Heideman, 1994) and it is for this reason that small mammals show such a diverse array of patterns of reproduction. Bernard and Hall, 1995). At temperate latitudes the climate is strongly seasonal and predictable, and most species and populations of small mammals use photoperiodic cues to trigger and inhibit reproductive activity (Clarke, 1985;Bronson, 1989;Nelson et al, 1992;Bronson and Heideman, 1994).…”