Relationships among rodent taxa as indicated by reproductive biology1

Abstract

Demonstrated that in rodents the duration of ontogenetic development (from conception to the age of eye openin) is allometrically related to the maternal body weight. The differences between actual developmental time and the expected time (counted for animals of that systematic position and that body weight) can be used as a tool to test phylogenetic relationships. As far as the relationships between sister‐taxa are concerned, the results of the present analysis corroborate the conclusions of modern classifications. A long developmental time (which means by implication also a long pregnancy and precocity) is couled with hystricognathy and hystricomorhy. These traits must be considered plesiomorphic and their occurrence suggests conservatism of articular taxa. Parallell (coupled) with adopting sciurognathy and, particularly, protrogomorpiy, sciuromorphy, and eventually, myomorphy, rodents were able to shorten their developmental times. In this way they could increase the reproductive rate and made their reproduction more efficient. Consequently the respective taxa radiated more rapidly and successfully.

Field evidence for colony size and aseasonality of breeding and in Ansell’s mole-rat,Fukomys anselli(Rodentia: Bathyergidae)

“…Our field data supports laboratory findings that Fukomys species studied to date (F. anselli (Burda 1989); F. damarensis (Bennett & Jarvis 1988;Bennett & Faulkes 2000); F. darling ) are aseasonal breeders with pups being born throughout the year. It is, however, noteworthy that within the more southerly occurring genus of Cryptomys, reproduction appears to be strictly seasonal, e.g.…”

Field evidence for aseasonality of reproduction and colony size in the Afrotropical giant mole-ratFukomys mechowii(Rodentia: Bathyergidae)

“…In all social Cryptomys and Fukomys species and in Heterocephalus there is a marked reproductive skew characteristic of cooperative breeders, whereby breeding is normally restricted to a single reproductive female and one or a few male consorts (Bennett & Jarvis 1988a;Burda 1989;Bennett et al 1994;Bennett & Aguilar 1995;Bennett & Faulkes 2000;Scharff et al 2001). A significant result in this study is the observation of plural breeding, with two breeding females present (and pregnant) in four of the 32 colonies.…”

“…The small litter size (two to four pups) produced by F. mechowii is also characteristic of other species of both Fukomys (Bennett & Jarvis 1988a;Burda, 1989;Bennett et al 1994;Bennett & Aguilar 1995;Scharff et al 2001) and Cryptomys (Bennett 1989;Malherbe et al 2004, Oosthuizen et al 2007. Among the social bathyergid genera Fukomys and Cryptomys, the species so far investigated all have relatively small litters (2-6 pups; Bennett et al 1991), compared to solitary species, e.g.…”

“…Our field data clearly support the laboratory findings that giant mole-rats do indeed breed continuously throughout the year. To date, all the studied species within the genus Fukomys have been reported to be aseasonal breeders producing offspring throughout the year: F. damarensis (Bennett & Jarvis 1988a,b;Bennett & Faulkes 2000), F. darlingi (Bennett et al 1994) and F. anselli (Burda 1989) By contrast, within the more southerly occurring genus Cryptomys, reproduction appears to be more seasonal, e.g. Cryptomys h. hottentotus (Spinks et al 1997(Spinks et al , 1999 and Cryptomys h. pretoriae (Janse van Rensburg et al 2002).…”

“…Georychus capensis, Bathyergus suillus, Bathyergus janetta and Heliophobius argenteocinereus (Sumbera et al 2003;Hart et al 2006;Oosthuizen & Bennett 2007), and social, e.g. Cryptomys and Fukomys (Bennett & Jarvis 1988a;Bennett 1989;Burda 1989;Spinks et al 1997Spinks et al , 1999Janse van Rensburg et al 2002. Until recently, the only published information on the reproduction of the giant mole-rat was derived from laboratory studies (Bennett & Aguilar 1995;Scharff et al 1999) and one small field study (Scharff et al 2001) in which reproduction was suggested to take place throughout the year, or from anecdotal reports from Ansell (1978) who captured young animals throughout the year.…”