Age of the Jeju pony (Equus caballus) at first reproduction: Potential costs for foals and mothers that first reproduce early in life

Abstract

In a related paper, we showed that mares that reproduced early in life tended to have higher fecundity because of a decrease in the duration of inter-birth intervals relative to mares that reproduced later in life. However, we know that young mares are subordinate to older mares. Hence, costs associated with low dominance rank might offset the benefits of earlier reproduction. We compared harassment of foals of female Jeju ponies that first reproduced at three years of age with that of foals of females that first reproduced at five years of age. As a consequence of their positions in the linear dominance hierarchy, foals born to and guarded by young mares were harassed more frequently than foals whose mothers were older when they first reproduced. A mare that reproduced early in life guarded her offspring more closely and intervened between her foal and neighboring mares more frequently than those mares which first reproduced when older. This need to guard their foals and the harm that might ensue from frequent harassment might counter-balance selection towards earlier reproduction in mares. © Japan Ethological Society and Springer 2009.