| Summary: | The reproductive ecology of Tenrec ecaudatus was studied on Praslin Island (4°20'S, 55°45'E) from November 1977 - September 1980. Ambient temperatures vary little, but tenrecs aestivate for approximately six months each year when food supply is lowest. Following cessation of the annual period of reproduction, they fatten rapidly immediately before aestivation, males earlier than females. Males may also aestivate earlier than females but always arouse approximately one month earlier. Circadian variation in body temperature (T<sub>B</sub>) of seasonally-active tenrecs is marked, with highest T<sub>B</sub> recorded during daily activity and lowest T<sub>B</sub> during rest. T<sub>B</sub> in active males is lower that at other times. Pregnant females can lower T<sub>B</sub> by up to 12°C without adversely affecting themselves or their conceptuses. Spontaneous arousal during aestivation may be endogenous. Testicular recrudescence to the completion of spermateliosis occurs and growth of ovarian follicles begins during aestivation. Spermatogenesis ontinues until December or January and inter-male competition for access to oestrous females is evident. Females conceive soon after arousal from aestivation. Ovarian follicles are relatively small and spermatozoa enter the theca of mature follicles during gentle extrusion of the granulosa and oocyte at ovulation, and intrafollicular fertilization may occur. Polyovular follicles contributed to at least 25% of pregnancies where more fetuses then corpora lutea (CL) were observed. CL form by extrusion, and mean number per-female was 10.4 ± 0.5 S.E. Most births occur in December, coinciding with peak food supply, but were recorded at any time of year. Fetus survival and litter size decreases after December. The relative size of the placenta accounts for 41% of variation in fetus survival and the number of implantations and surviving fetuses declines with maternal age. Intra-litter variation in fetus weight extends to 273% and 74% of females resorb one or more fetuses. Mean number of implantations on Praslin (9.7 ± 0.5 S.E.) was lower than previously recorded in Madagascar (17.1 ± 1.9 S.E.). The energetic demands of lactation result in the mother and her offspring extending feeding into daylight hours. It is suggested that the striped colouration of juveniles and the darker colouration in adult females compared to adult males arose as cryptic colouration in response to increased risk of predation due to foraging in daylight hours. It is hypothesised that Hemicentetes may be a paedogenic form which has arisen from a Tenrec-like ancestor.
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