Reproductive biology

Little is known about the reproductive biology of most members of Insectivora. Those with short life spans, the majority of the shrew species for example, produce several litters a year while longer living insectivores, such as tenrecs, mate only once a year. Insectivores produce as few as one offspring per litter but some tenrecs can have as many as 32 young at one time (the maximum offspring produced by mammals). Gestation periods vary from two weeks to two months. The same is true for the length of time the young nurse. The number of teats ranges from two to 24 and their location on the body depends on the species. Many male insectivores have testes in the abdominal cavity lying close to the opening of the perineum. Moles and tenrecs have a baculum (penis bone). Courtship and mating practices, which have seldom been observed but are probably polygynous, tend to be short and to the point lasting as little as a few seconds in some species, but lasting hours in other species. Some young, such as certain tenrecs, are born with hair, able to run around immediately following birth and are totally independent within weeks. On the other hand, moles are born completely naked save for a few vibrissae and guard hairs. The latter are helpless and highly dependent on the mother for several months.

There are some unusual reproductive and parenting habits among insectivorans. The female lesser hedgehog tenrec (Echinops telfairi), for example, emits odors during the mating season that cause males to secrete a milky white substance from glands near the eyes. Their mating ritual can last several hours, as it does among certain species of Erinaceinae (spiny hedgehogs). The male hedgehog tenrec stays with his mate up to a few hours before young are born, then he leaves and stays away as long as the young are dependent on their mother. The male spiny hedgehog must be persistent in his courtship as he often ends up chasing after his mate for several hours before she allows him to mount. The female spiny hedgehog flattens its spines during mating, if she is receptive. Because the spines are slippery, the male must hold on to his mate's shoulder with his teeth. Shrews are known for their antagonistic conduct towards one another, even during mating. Among many shrews, exposure to a conspecific (member of the same species) immediately triggers aggressive behavior. The sexual odors emitted by both parties during courtship eventually overpower the tendency towards violence, allowing copulation to take place.

The offspring of the white-toothed shrew (Crocidura leu-codon), and musk shrews (Suncus murinus) or pygmy shrews (Sorex hoyi)—anywhere from three to seven at a time—are led by their mother in line formation, also known as caravaning. The first young shrew grabs a mouthful of hair right above its mother's tail with its teeth. The siblings follow the example with each other down the line.

A yellow streaked tenrec (Hemicentetes semispinosus) showing defensive behavior. (Photo by Harald Schütz. Reproduced by permission.)

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