Superdelayed parturition in armadillos: a new mammalian survival strategy

Abstract

Summary. Armadillos are generally believed to have a gestation period of 8-9 months that includes a 3-to 4-month period of embryonic diapause. Nevertheless, 21 fe males bore litters 13-24 months after capture and subsequent isolation from males. Two of these animals were pregnant in successive years. Evidence is presented that this is a facultative survival mechanism, induced by stress, that has not been previously reported among mammals.Armadillos (Dasypus novemcinctus) are placental mammals (Order Xenarthra) that are usually monestrous and monovular. I In North America, parous fe males ovulate during July and August and nulliparous animals in November. After summer ovulation and mating, embryos develop to the blastocyst stage and then enter a diapause period of 3-4 months. Implantation of a single blastocyst usually takes place in late November or early December, I after which the cell mass buds twice to yield 4 embryos.2.3 Monozygous quadruplets are born in the spring about 5 months after implantation. I Thus gestation is believed to last for 8-9 months including embryonic diapause.However, we have found that some females bear young 1-2 years after the generally accepted time fo r parturition, a phenomenon not previously reported among mammals. Materials and methodsThis finding resulted from the use of wild-caught armadillos in leprosy research4 so that large numbers of them are housed in laboratories throughout the world. To minimize injuries, all animals in our colonies in Florida and England were housed separately in plastic cages fo r 1-3 years before they were killed for harvest of leprosy bacilli. Cage design and the protocols used precluded copulation after capture. These procedures are described in detail elsewhere.s Animals were collected in groups of 10-40 in Central Florida from 1979 to June 1986. The dates of capture were governed by the requirements of the leprosy programme; therefore, sampling of the wild population was not uniform from month to month.

Genetic Maternity and Paternity in a Local Population of Armadillos Assessed by Microsatellite DNA Markers and Field Data

“…Second, after litters emerge more than one female during a breeding season, but females typically pair with just one male (McDonough from their natal burrows, they appear to have little contact with the mother (McDonough and Loughry 1997Loughry ), 1992Loughry , 1997. Implantation of the fertilized embryo is delayed but usually occurs by late fall or early winter so behavioral associations between a female and a set of juveniles that could lead to inferences about maternity (Storrs et al 1988), with females giving birth to litters of genetically identical quadruplets the following spring are rare. Finally, home-range overlap between a female and a set of young is also not a reliable indicator of ma- (Newman and Patterson 1910;Patterson 1913;Storrs and Williams 1968;Prodöhl et al 1996).…”

Circulating concentrations of gonadal and adrenocortical hormones in wild nine-banded armadillos (Dasypus novemcinctus)

“…During this time, females ovulate a single egg (Enders 1960). After fertilization, there is a variable period of delayed implantation (Talmage et al 1954, Storrs et al 1988, Peppler 2008) that usually ends sometime in late fall (Hamlett 1932, Talmage et al 1954, Enders 1966. Gestation lasts ∼134 days with birth normally occurring in March-April (Hamlett 1932, Enders 1966.…”

Correlates of reproductive success in a population of nine-banded armadillos

“…Nine-banded armadillos (Dasypus novemcinctus) are relatively asocial, nocturnal, burrowing mammals (Newman 1913;Kalmbach 1943;Taber 1945;Talmage and Buchanan 1954;Galbreath 1982;McBee and Baker 1982). Breeding usually occurs during the summer, with delayed implantation of the blastocyst occurring in autumn (Hamlett 1932;Enders 1966;Storrs et al 1988;McDonough 1992). Young are born in litters of genetically identical quadruplets the following spring (Newman and Patterson 1910;Patterson 1913;Hamlett 1932;Enders 1966;Storrs and Williams 1968;Prodöhl et al 1996) and first emerge from their natal burrows in May or early June.…”