Size dependence in non-sperm ejaculate production is reflected in daily energy expenditure and resting metabolic rate

Abstract

A number of minor errors were published in J. Exp. Biol. 218, 1410-1418 The corrected sections are reproduced below, with changes highlighted in bold. These changes do not affect the conclusions of the paper. RESULTS Metabolic substrates: respiratory quotientMean respiratory quotient (RQ=VĊ O2 /VȮ 2 , where VĊ O2 is the rate of CO 2 production and VȮ 2 is the rate of O 2 consumption) across treatments and size classes was 0.743. Mean RQ of the mating males (median=0.71) was significantly lower than that of the courting males (median=0.76) [Kruskal-Wallis test, K 1 =24.091 (where the subscript 1 indicates d.f.), P<0.001]. A non-parametric test was used because these data failed a normality test (Shapiro-Wilk, P<0.05). This difference in RQ between courting and mating males was driven by small courting males having a significantly higher RQ than small mating males (Kruskal-Wallis test, K 3 =31.394, P<0.001; multiple comparisons using Dunn's method; Fig. 5). This suggests that small, mating males were using different metabolic substrates after mating from those used by the small, courting males. The shift in RQ, seen only in small males (Fig. 5), provides support for the hypothesis that smaller males are investing in plug production, as a shift in the substrates used in metabolism could be due to shunting resources to plug production from muscular activity (i.e. mate searching and courtship).The authors apologise for any inconvenience this may have caused. ABSTRACTThe non-sperm components of an ejaculate, such as copulatory plugs, can be essential to male reproductive success. But the costs of these ejaculate components are often considered trivial. In polyandrous species, males are predicted to increase energy allocation to the production of non-sperm components, but this allocation is often condition dependent and the energetic costs of their production have never been quantified. Red-sided garter snakes (Thamnophis sirtalis parietalis) are an excellent model with which to quantify the energetic costs of non-sperm components of the ejaculate as they exhibit a dissociated reproductive pattern in which sperm production is temporally disjunct from copulatory plug production, mating and plug deposition. We estimated the daily energy expenditure and resting metabolic rate of males after courtship and mating, and used bomb calorimetry to estimate the energy content of copulatory plugs. We found that both daily energy expenditure and resting metabolic rate were significantly higher in small mating males than in courting males, and a single copulatory plug without sperm constitutes 5-18% of daily energy expenditure. To our knowledge, this is the first study to quantify the energetic expense of size-dependent ejaculate strategies in any species.

Developmental environment mediates male seminal protein investment in Drosophila melanogaster

“…Females mate faster with large than with small males (the present study and Pitnick ), and small males lose out in competition with large males (Partridge, Ewing & Chandler ), so it may pay small males to invest heavily in any matings achieved, as has been argued for similar patterns found in garter snakes ( Thamnophis sirtalis parietalis ; Friesen et al . ). In contrast, large males that may have multiple mating opportunities might risk ejaculate depletion if they do not partition their ejaculate (Hihara ; Linklater et al .…”

“…However, there is currently limited data available on the costs of Sfp production (Perry, Sirot & Wigby ; Friesen et al . ; Sirot & Wolfner ). Furthermore, traits involved in post‐copulatory interactions are often subject to strong stabilizing selection (e.g.…”

The molecular basis and reproductive function(s) of copulatory plugs

“…The very existence of male mate choice, rather than indiscriminant mating (Drickamer et al, ; Gowaty et al, ; Edward and Chapman, ), and evidence that males adjust their ejaculates when presented with sub‐optimal mating opportunities (Pizzari et al, ; Delbarco‐Trillo and Ferkin, ; Ramm and Stockley, ; Lüpold et al, ; DelBarco‐Trillo, ; Ramm et al, ) together imply that ejaculates are physiologically expensive and are conserved whenever possible (Parker, ; Parker and Pizzari, ). Indeed, direct calorimetric study revealed that a single copulatory plug in garter snakes might represent 5–18% of an animal's daily energy budget (Friesen et al, ). To our knowledge, no equivalent study has been performed in a mammal, partly because it is currently not possible to separate the cost of seminal fluid versus spermatogenesis, as can be achieved in snakes (Friesen et al, ).…”

“…Indeed, direct calorimetric study revealed that a single copulatory plug in garter snakes might represent 5–18% of an animal's daily energy budget (Friesen et al, ). To our knowledge, no equivalent study has been performed in a mammal, partly because it is currently not possible to separate the cost of seminal fluid versus spermatogenesis, as can be achieved in snakes (Friesen et al, ). Nevertheless, the relatively high rate of protein turnover by seminal vesicles may enable the dynamic allocation of resources by mammals (Claydon et al, ).…”

Sexual coloration and sperm performance in the Australian painted dragon lizard, Ctenophorus pictus

“…sperm and seminal fluid production; e.g. Dewsbury, ; Olsson et al ., ; Friesen et al ., ) and precopulatory sexually selected traits (i.e. weapon development, display traits and associated behaviours; e.g.…”