Lank David B, Rockwell Robert F, Cooke Fred
Department of Biology, Queen's University, Kingston, ON, K7L 3N6, CANADA.
Department of Biology, The City College, New York, NY, 10031, USA.
Evolution. 1990 Sep;44(6):1436-1453. doi: 10.1111/j.1558-5646.1990.tb03837.x.
The reproductive efficiency, defined as the number of breeding recruits produced per egg laid; of intraspecific nest parasites; of hosts in parasitized nests; and of unparasitized nesting females, was measured for 14 years for lesser snow geese Anser caerulescens caerulescens nesting near Churchill, Manitoba, Canada. Relative efficiencies were 0.71-0.88, 0.91, and 1.0 for eggs of parasites, hosts, and unparasitized birds, respectively. Differences in the hatching probabilities of the three classes of eggs produced the efficiency differences. Parasitic success was limited by the parasites' failure to place more eggs than expected by chance into nests at the appropriate time relative to host incubation. Host nesting success was lower when more than one parasitic egg was added to the clutch. No differences in gosling survival and breeding recruitment probabilities were detected among any categories of goslings. Thus, hatching parasitic young are at no disadvantage relative to parental young, and there is no support for the hypothesis that increased success of host young at later stages of reproduction might offset negative effects at the egg stage. The hatching efficiency of parasitic eggs declined more rapidly than that of parental eggs as the parasitism rate increased. Efficiencies were similar when 3-4% of the eggs laid per year were parasitic, but relative parasitic efficiency was significantly lower when the parasitism rate was 8-9% or more. Using ancillary information and assumptions about the fecundity, viability, and behavioral flexibility of parasitic and parental females, we conclude that intraspecific nest parasitism could compete with nesting as a reproductive strategy in this population. The conditional use of parasitism by a large component of the population in certain years, however, combined with negative-frequency dependent success, limits the potential spread of a purely parasitic strategy in this population.
对在加拿大曼尼托巴省丘吉尔附近筑巢的小雪雁（Anser caerulescens caerulescens）的繁殖效率进行了为期14年的测量。繁殖效率的定义为：每产下一枚卵所产生的繁殖新个体数量，包括种内巢寄生者的繁殖效率、被寄生巢中宿主的繁殖效率以及未被寄生的筑巢雌鸟的繁殖效率。寄生虫卵、宿主卵和未被寄生鸟类卵的相对繁殖效率分别为0.71 - 0.88、0.91和1.0。这三类卵孵化概率的差异导致了繁殖效率的差异。寄生成功率受到限制，原因是寄生虫未能在相对于宿主孵化的适当时间，比随机预期的数量更多地将卵放入巢中。当一窝卵中添加了不止一枚寄生卵时，宿主筑巢成功率会降低。在任何类别小鹅中，未检测到小鹅存活率和繁殖新个体概率的差异。因此，孵化出的寄生幼雏相对于亲本幼雏并无劣势，并且没有证据支持这样的假设，即宿主幼雏在繁殖后期更高的成功率可能会抵消卵阶段的负面影响。随着寄生率的增加，寄生卵的孵化效率比亲本卵下降得更快。当每年产下的卵中有3 - 4%为寄生卵时，效率相似，但当寄生率为8 - 9%或更高时，相对寄生效率显著降低。利用关于寄生和亲本雌鸟的繁殖力、生存能力以及行为灵活性的辅助信息和假设，我们得出结论，种内巢寄生在这个种群中可能作为一种繁殖策略与筑巢相互竞争。然而，在某些年份种群中很大一部分有条件地使用寄生，再加上负频率依赖的成功率，限制了纯粹寄生策略在这个种群中的潜在传播。
