Response to selection and realized heritability of sperm length in the yellow dung fly (Scathophaga stercoraria)

Abstract

Sperm length shows considerable phenotypic variation both inter-and intra-specifically, but a general explanation for this variation is lacking. In addition, our understanding of the genetic variation underlying sperm length variation is also limited because there have been few studies on the genetics of sperm size. One factor that could explain the variation in sperm length is that length influences sperm competitiveness, and there is some evidence for this. However, in yellow dung flies (Scathophaga stercoraria), microevolutionary responses to experimental variation at levels of sperm competition indicate that sperm length does not influence sperm competitiveness, although this lack of response may simply indicate sperm length lacks evolutionary potential (that is, it is constrained in some way), in spite of evidence that sperm length is heritable. Here we report on a laboratory study, in which we artificially selected upwards and downwards on sperm length in S. stercoraria. We found that sperm length significantly diverged after four generations of selection, but the response to selection was asymmetrical: upward selection generated a rapid response, but downward did not. We estimated the realized heritability of sperm length to be approximately 50%, which is consistent with previous sire-son estimates. We also assessed the fertility of males from upward and downward lines and found they did not differ. Results are discussed in the context of sperm competition.

Genetic and Genomic Response to Selection for Food Consumption in Drosophila melanogaster

“…Traits that are components of fitness are expected to have reduced additive genetic variance (Falconer and Mackay 1996; Fisher 1999), mostly attributable to alleles segregating due to mutation-selection balance (Falconer and Mackay 1996; Fisher 1999). Thus, there will be little selection response in the direction of increased fitness, but response in the direction of decreased fitness (Cunningham and Siegel 1978; Mackay et al 2005; Vishalakshi and Singh 2009; Dobler and Hosken 2010). From this, we infer that increased food consumption is deleterious in D. melanogaster .…”

Moderate heritability and low evolvability of sperm morphology in a species with high risk of sperm competition, the collared flycatcher Ficedula albicollis

“…The genetic sources of phenotypic variation in sperm traits have been studied in several species of insects (Baer et al, 2006;Dobler & Hosken, 2010;Morrow & Gage, 2001a;Simmons & Kotiaho, 2002;Ward, 2000) and mammals (Napier, 1961;Woolley, 1971;Woolley & Beatty, 1967), but as yet only in a single bird species: captive zebra finches (Birkhead, Pellatt, Brekke, Yeates, & Castillo-Juarez, 2005;Kim et al, 2017;Knief et al, 2017;Mossman, Slate, Humphries, & Birkhead, 2009). Heritability estimates of sperm morphology from these studies were usually high, with often more than 50% of the phenotypic variation in sperm morphological traits attributable to additive genetic effects (Table 1).…”

Heat stress but not inbreeding affects offensive sperm competitiveness in Callosobruchus maculatus

“…; Dowling et al. ; Dobler and Hosken ), estimates for heritability and additive genetic variance in sperm‐competitive performance are generally modest (reviewed in: Simmons and Moore ). The influence of environmental effects on sperm competitive success is increasingly recognized (e.g., oviposition site availability: Eady et al.…”

“…As do the quantities of seminal fluid and accessory gland products that can have profound effects on sperm competition by modifying female reproductive behavior (Chapman 2001;Simmons 2001;Gillott 2003). Although many components of ejaculates have well-established genetic bases (Hales et al 1989;Ducrocq and Humblot 1995;Swanson et al 2001;Birkhead et al 2005;Dowling et al 2007;Dobler and Hosken 2009), estimates for heritability and additive genetic variance in sperm-competitive performance are generally modest (reviewed in: Simmons and Moore 2009). The influence of environmental effects on sperm competitive success is increasingly recognized (e.g., oviposition site availability: Eady et al 2004;larval density, nutrition: Amitin and Pitnick 2007;adult density: Crean and Marshall 2008;sperm competition risk: DelBarco-Trillo 2011;immune insult: McNamara et al 2013).…”