Experimental evidence that high levels of inbreeding depress sperm competitiveness

Abstract

The effects of inbreeding on sperm quantity and quality are among the most dramatic examples of inbreeding depression. The extent to which inbreeding depression results in decreased fertilization success of a male’s sperm, however, remains largely unknown. This task is made more difficult by the fact that other factors, such as cryptic female choice, male sperm allocation and mating order, can also drive patterns of paternity. Here, we use artificial insemination to eliminate these extraneous sources of variation and to measure the effects of inbreeding on the competitiveness of a male’s sperm. We simultaneously inseminated female guppies (Poecilia reticulata) with equal amounts of sperm from an outbred (f = 0) male and either a highly (f = 0.59) or a moderately inbred (f = 0.25) male. Highly inbred males sired significantly fewer offspring than outbred males, but share of paternity did not differ between moderately inbred and outbred males. These findings therefore confirm that severe inbreeding can impair the competitiveness of sperm, but suggest that in the focal population inbreeding at order of a brother–sister mating does not reduce a male’s sperm competitiveness.

Inbreeding depression of sperm traits in the zebra finch Taeniopygia guttata

“…2006; Zajitschek et al. 2009). In birds, wide interspecific variation in levels of sexual promiscuity has been documented (Griffith et al.…”

“…In contrast with studies on invertebrates and plants, most such studies have not used controlled breeding designs (e.g., full‐sib mating) to produce inbred and outbred individuals raised under standard conditions (but see Zajitschek et al. 2009; Mehlis et al. 2012; Gasparini et al.…”

Pattern of inbreeding depression, condition dependence, and additive genetic variance in Trinidadian guppy ejaculate traits

“…Our result is in agreement with the previous work on a feral (Australian) guppy population, in which significant inbreeding depression in sperm production was found after two generations of full-sib matings (Zajitschek and Brooks 2010). Another study on the same guppy population revealed that sperm competitiveness is reduced only after four generations of full-sib mating when the number of sperm inseminated is experimentally controlled for using artificial insemination (Zajitschek et al 2009). These two results indirectly suggest that the pattern of directional selection for sperm number and velocity may be similar in our and in the Australian population studied by Zajitschek and colleagues (although sperm quality has not been directly measured in the latter).…”

Hatchery selection may depress the number of motile sperm but intensify selection for their swimming velocity in the Arctic charr

“…On the other hand, the fact that captive breeding practices increase the risk of inbreeding suggests that potential decline in sperm quality may be directly related to inbreeding depression. Supporting this view, the detrimental effects of inbreeding on semen traits have been well demonstrated: It reduces the ejaculate volume, number of motile sperm and/or number of normal sperm (Roldan et al 1998;Gomendio et al 2000;van Eldik et al 2006;Gage et al 2006;Fitzpatrick and Evans 2009;Zajitschek et al 2009). However, selection and inbreeding often have opposite effects on fitness-related traits, and it has been demonstrated that selection can delay or hinder the detrimental effects of inbreeding (Connor and Bellucci 1979;Wade et al 1996).…”

“…Inbreeding has severe effects on individual fitness (e.g. Hedrick and Kalinowski 2000;Drayton et al 2007) and traits that are closely related to reproduction (Zajitschek et al 2009). In addition to the loss of genetic diversity, captive breeding may also cause selective changes in various phenotypic traits (e.g.…”