Evolution of reproductive seasonality in bears

Abstract

1. Of the eight species of Ursidae, six are currently at risk of extinction and the remainder face significant risks to their future survival. One of the greatest threats to bears is humanimposed environmental alteration (e.g. global warming, chemical pollutants, deforestation). An examination of the reproductive biology and phylogeny of the Ursidae reveals reproductive seasonality as a probable adaptation to adverse environmental conditions. 2. Seven of the eight extant species exhibit distinct mating and birth seasons, with the most ancient species evolving facultative seasonality as an adaptation to the increasingly seasonal climate of the Pliocene. The remainder of the extant species evolved during the Pleistocene glaciations, under conditions of severe seasonal food restriction. Under these conditions, an obligate mode of seasonality emerged and persists to the present. 3. Knowledge of the natural history of seasonal reproduction in the ursids and how it evolved in response to global climatic change provides a context for understanding the ramifications of current environmental change on the reproduction of these important species.

Unique biphasic progestagen profile in parturient and non-parturient giant pandas (Ailuropoda melanoleuca) as determined by faecal hormone monitoring

“…Doing so permitted careful examination of the relatively modest, yet significant primary progestagen rise that characterized the immediate post-oestrual interval, even in unmated females. This finding confirmed previous assertions by others (Monfort et al 1989, Mainka et al 1990, Steinman et al 2006, Spady et al 2007) that luteal formation was spontaneous and obligate in this species. Whereas the duration of the initial progestagen rise varied highly among individuals and across years, we found great consistency in the magnitude and duration of the shorter, hyperelevated secondary hormonal rise.…”

“…There has been little attention directed at understanding the prolonged luteal phase in pregnant versus non-pregnant individuals. Of ten reports on this topic, only three giant pandas in total have been monitored for urinary progestagen profiles from ovulation to parturition or through a non-parturient phase (sometimes referred to as 'pseudopregnancy'; Bonney et al 1982, Hodges et al 1984, Chaudhuri et al 1988, Masui et al 1989, Monfort et al 1989, McGeehan et al 2002, Narushima et al 2003, Dehnhard et al 2006, Steinman et al 2006, Spady et al 2007. In these cases, a secondary urinary progestagen rise has occurred 74-122 days after the end of oestrus (Steinman et al 2006) that has suggested a shift in hormonal source, perhaps related to nidation.…”

“…In these cases, a secondary urinary progestagen rise has occurred 74-122 days after the end of oestrus (Steinman et al 2006) that has suggested a shift in hormonal source, perhaps related to nidation. The giant panda has long been considered to experience delayed implantation (Hodges et al 1984, Monfort et al 1989, Zhang et al 2009), a strictly mammalian strategy prominent in carnivores, especially ursids (Hamlett 1935, Conaway 1971, Weir & Rowlands 1973, Renfree & Calaby 1981, Mead 1989, Sandell 1990, Lindenfors et al 2003, Spady et al 2007. After fertilization, the embryo is sustained as a blastocyst until an unidentified trigger stimulates implantation and resumption of development (Renfree & Calaby 1981, Mead 1989, Sandell 1990).…”

Endocrine milieu of perioestrus in the giant panda (Ailuropoda melanoleuca), as determined by non-invasive hormone measures

“…1998;Lindburg etal. 2001;McGeehan et al 2002;Durrant et al 2002;Steinman et al 2006), and for other Ursidae (Ferguson and McLoughlin 2000;Spady et al 2007). For the two most intensively monitored giant pandas, the data revealed that there was some variation in the onset of oestrus over time, and sexual receptivity appeared to occur over a 1.9-7.5-week interval from year-to-year in a given female.…”

Humming in bears: a peculiar sustained mammalian vocalization

“…All living ursid species in the subfamilies Tremarctinae and Ursinae are the product of a relatively recent Plio-Pleistocene radiation that took place on the northern continents (Hunt 1996, Spady et al 2007). Marked seasonal differences in the availability of food may have led to the evolution of winter dormancy in this radiation.…”