School of Life and Environmental Sciences, University of Sydney, Sydney, New South Wales 2006, Australia.
School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia.
Biol Lett. 2019 Jul 26;15(7):20190339. doi: 10.1098/rsbl.2019.0339. Epub 2019 Jul 24.
As a colonizing species expands its range, individuals at the invasion front experience different evolutionary pressures than do those at the range-core. For example, low densities at the edge of the range mean that males should rarely experience intense sperm competition from rivals; and investment into reproduction may trade-off with adaptations for more rapid dispersal. Both of these processes are predicted to favour a reduction in testis size at the invasion front. To explore effects of invasion stage in Australian cane toads (Rhinella marina), we collected and dissected 214 adult males from three regions: one in the species' range-core (northeastern Australia), and two from invasion fronts (one in northwestern Australia and one in southeastern Australia). Despite the brief duration of separation between toads in these areas (approx. 85 years), testis masses averaged greater than 30% higher (as a proportion of body mass) in range-core males than in conspecifics sampled from either vanguard of the invasion. Previous work has documented low reproductive frequencies in female cane toads at the invasion front also, consistent with the hypothesis that evolutionary and ecological pressures unleashed by an invasion can favour relatively low resource allocation to reproduction in both sexes.
随着一个殖民物种的分布范围扩大，处于入侵前沿的个体所经历的进化压力与处于分布核心的个体不同。例如，在分布范围的边缘密度较低意味着雄性很少会受到来自竞争对手的强烈精子竞争；繁殖的投入可能与更快速扩散的适应能力相权衡。这两个过程都预计会导致入侵前沿的睾丸体积减小。为了探索澳大利亚甘蔗蟾蜍（Rhinella marina）的入侵阶段的影响，我们从三个地区收集并解剖了 214 只成年雄性：一个在该物种的分布核心区（澳大利亚东北部），两个在入侵前沿（一个在澳大利亚西北部，一个在澳大利亚东南部）。尽管这些地区的蟾蜍分离时间很短（约 85 年），但分布核心区雄性的睾丸质量平均比从入侵前沿采集的同种蟾蜍高出 30%以上（相对于体重的比例）。之前的研究记录了入侵前沿雌性甘蔗蟾蜍的繁殖频率较低，这与入侵释放的进化和生态压力有利于两性相对较低的资源分配给繁殖的假设一致。
