Testes size in birds: quality versus quantity - assumptions, errors, and estimates
Testes size in birds: quality versus quantity - assumptions, errors, and estimates
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DOI：
10.1093/beheco/arl076
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发表时间：
2007-01-01
影响因子：
2.4
通讯作者：
Birkhead, Tim R.
中科院分区：
文献类型：
--
作者：
Calhim, Sara;Birkhead, Tim R.
在广泛的无脊椎动物和脊椎动物分类群中，相对较大的睾丸与雌性和/或雄性乱交有关(例如，哺乳动物：Short 1979； Harcourt等人1981；Harvey和Harcourt 1984； Kenagy和Trombulak 1986； Hosken 1997, 1998；但参见Heske和Ostfield 1990；鸟类：Cartar 1985； Møller 1991； Birkhead和Møller 1992； Møller和Briskie 1995；爬行动物：Olsson和Madsen 1998；两栖动物：Jennions和Passmore 1993； Byrne等人2002；鱼类：Stockley等人1997；Balshine et al. 2001；蝴蝶：盖奇1994；果蝇：Pitnick 1996；棘头虫：Poulin and Morand 2000)。对于睾丸大小的种间变异，人们提出了两种普遍的假说：1)精子竞争（Parker 1970）和2)精子消耗（Short 1981）。现有数据表明，在鸟类睾丸大小的进化过程中，精子竞争可能是一种比精子消耗更重要的选择力量（例如，鸟类：Møller 1991； Birkhead and Møller 1992）。因此，物种特异性睾丸大小数据被用作比较研究中精子竞争水平的方便且被认为可靠的指标，特别是鸟类（参见Møller 1991； Briskie and montgomery 1992; Møller and Briskie 1995; Stutchbury and Morton 1995; Dunn et al. 2001; Morrow et al. 2003; Garamszegi et al. 2005; Pitcher et al. 2005）。估计睾丸的大小在性腺位于内部并表现出巨大的季节变化的分类群中尤其困难，如鸟类（Lofts and Murton 1973）和爬行动物（James and Shine 1985）。其中一个主要的困难是，要进入性腺，必须使用侵入性方法，如解剖或剖腹手术（例如，Wingfield和Farner 1976），尽管随着技术的进步，可以使用非侵入性磁共振成像技术（Czisch et al. 2001）。关于睾丸大小的数据可以从各种来源获得，从对特定物种的详细实地研究到博物馆的皮肤。鸟类睾丸大小的比较研究使用了不同的估计方法，几种数据来源，以及迄今为止未经检查的方法假设来编制特定物种的睾丸大小估计。我们的目的不是批评以前的工作，这些工作在尝试获得广泛的鸟类分类群的这些估计方面一直处于领先地位，而是要1)证明这些估计的可靠性和准确性在研究之间和研究内部是如何以及为什么不同的；2)指出鸟类睾丸大小数据的质量如何影响在比较分析中使用更大的低质量数据集时获得的结果。所有的统计和模拟分析均使用rv . 2.0进行。1 （R Development Core Team 2004）和(S) MATR （Falster et al. 2003）计算机软件包。除非另有说明，否则结果以标准误差的平均值表示。
Across a wide range of both invertebrate and vertebrate taxa, relative larger testes are associated with female and/or male promiscuity (eg, mammals: Short 1979; Harcourt et al. 1981; Harvey and Harcourt 1984; Kenagy and Trombulak 1986; Hosken 1997, 1998; but see Heske and Ostfield 1990; birds: Cartar 1985; Møller 1991; Birkhead and Møller 1992; Møller and Briskie 1995; reptiles: Olsson and Madsen 1998; amphibians: Jennions and Passmore 1993; Byrne et al. 2002; fish: Stockley et al. 1997; Balshine et al. 2001; butterflies: Gage 1994; Drosophila flies: Pitnick 1996; acanthocephalan worms: Poulin and Morand 2000). Two general hypotheses have been proposed to explain interspecific variation in testes size: 1) sperm competition (Parker 1970) and 2) sperm depletion (Short 1981). Available data suggest that sperm competition may be a more important selective force than sperm depletion in the evolution of avian testes size (eg, in birds: Møller 1991; Birkhead and Møller 1992). As a result, species-specific testes size data have been used as convenient and assumedly reliable index of sperm competition levels in comparative studies, particularly of birds (see, eg, Møller 1991; Briskie and Montgomerie 1992; Møller and Briskie 1995; Stutchbury and Morton 1995; Dunn et al. 2001; Morrow et al. 2003; Garamszegi et al. 2005; Pitcher et al. 2005). Estimating testes size is particularly difficult in taxa where the gonads are located internally and show enormous seasonal changes in size as in birds (Lofts and Murton 1973) and reptiles (James and Shine 1985). One of the main difficulties is that to gain access to the gonads, one must use invasive approaches, such as dissection or laparotomy (eg, Wingfield and Farner 1976), although as technology improves it may be possible to use noninvasive magnetic resonance imaging techniques (Czisch et al. 2001). Data on testes size are available from a variety of sources, from detailed field studies of particular species to museum skins. Comparative studies of avian testes size have used different estimation methods, several sources of data, and hitherto unchecked methodological assumptions to compile species-specific testes size estimates. Our aim is not to criticize previous work, which has been pioneering in its attempts to obtain these estimates for a wide range of avian taxa, but rather to 1) demonstrate how and why the reliability and accuracy of those estimates differ both across and within studies and 2) point out how the quality of avian testes size data might affect the results obtained when larger, low-quality data sets are used in comparative analyses. All the statistical and simulation analyses were conducted using R v. 2.0. 1 (R Development Core Team 2004) and (S) MATR (Falster et al. 2003) computer software packages. Results are presented as means with standard errors, unless specified otherwise.