Sex ratios, intersexuality and sex change in copepods

Gusmão, Felipe; McKinnon, A. David

doi:10.1093/plankt/fbp059

Cited by 78 publications

(74 citation statements)

References 56 publications

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“…When late-stage copepodites change sex, this is typically demonstrated by morphological abnormalities of the genital segment and P5, and such indicators were never found in our sampling program at L4. Indeed, many field reports of intersex give occurrence as being in the low single-digit percentages (Hirst 1996;Gusmã o and McKinnon 2009). An exception is Liang and Uye (1996b, pg.…”

Section: Discussionmentioning

confidence: 99%

“…By contrast, in the calanoid copepod Acartia, a chromosomal mechanism of sex determination has been reported, with males being heterogametic (XO) and females homogametic (XX) (Goswami and Goswami 1974;Lecher et al 1995). A variety of mechanisms to explain ESD, which could act in different parts of the developmental life history, have been proposed (Gusmã o and McKinnon 2009). Given these issues, we need to determine in which stage(s) the sex ratio skew arises in pelagic copepods.…”

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confidence: 99%

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Does predation controls adult sex ratios and longevities in marine pelagic copepods?

Hirst

Bonnet²,

Conway

et al. 2010

Limnology & Oceanography

117

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We assess the causes of adult sex ratio skew in marine pelagic copepods by examining changes in these ratios between the juveniles and adults, sexual differences in juvenile stage durations, and mortality rates of adults in the field and laboratory (when free from predators). In the field, late copepodite stages (CIV and CV) commonly have sex ratios that are either not significantly different from equity (1 : 1), or slightly male biased. By contrast, in adults, these ratios are commonly significantly biased toward female dominance. Sex ratio skews are therefore primarily attributable to processes in adults. Members of the non-Diaptomoidea have especially skewed adult ratios; in the members Oithonidae and Clausocalanidae this is not generated from differences between male and female adult physiological longevity (i.e., laboratory longevity when free of predators). In the genera Acartia, Oithona, and Pseudocalanus, we estimate that predation mortality contributed $ 69% of the field mortality rate in adult males, whereas in Acartia, Oithona, and Calanus adult females, this is $ 36%. We conclude that (1) adult sex ratio skew in pelagic copepods is primarily due to differential mortality of the sexes in the adult stage and not in juveniles, (2) mortality rates of adult Acartia, Pseudocalanus, and Oithona are dominated by predation mortality rather than physiological longevity (except under extreme food limitation), and (3) in Pseudocalanus and Oithona, elevated mortality rates in adult males to females is predominantly due to higher predation on males. Our work demonstrates that we now need to develop a more comprehensive understanding of the importance of feeding preferences in predators.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Does predation controls adult sex ratios and longevities in marine pelagic copepods?

Hirst

Bonnet²,

Conway

et al. 2010

Limnology & Oceanography

117

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“…As a result, the sex ratio may change through the breeding season. In nature, the adult sex ratio can be determined by several other factors besides differential mortality rates; for example, environmental sex determination (ESD) governed by food conditions (Fleminger 1985;Korpelainen 1990;Irigoien et al 2000) or intersexuality (Gusmao and McKinnon 2009). The cost of breeding is a function of the mortality experienced in the 'time out' phase.…”

Section: Modelmentioning

confidence: 99%

Optimal mate choice patterns in pelagic copepods

2012

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The importance of sexual selection for the evolution, dynamics and adaptation of organisms is well known for many species. However, the topic is rarely studied in marine plankton, the basis of the marine food web. Copepods show behaviors that suggest the existence of sexually selected traits, and recent laboratory experiments identified some selected morphological traits. Here, we use a 'life history-based' model of sex roles to determine the optimal choosiness behavior of male and female copepods for important copepod traits. Copepod females are predicted to be choosy at population densities typically occurring during the main breeding season, whereas males are not. The main drivers of this pattern are population density and the difference in non-receptive periods between males and females. This suggests that male reproductive traits have evolved mainly due to mate competition. The model can easily be parameterized for other planktonic organisms, and be used to plan experiments about sexual selection.

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“…In dioecious species, sex ratios are predicted to be close to unity if the investment in the production of each sex is the same (Charnov 1982). However, skewed sex ratios are often observed in populations with separate sexes (Charnov 1982, Kiørboe 2006, Gusmão & McKinnon 2009, Hirst et al 2010. Skewed sex ratios can be the result of various factors, such as the presence of sex allocation-distorting elements (the occurrence of selfish genetic elements and endosymbionts such as Wolbachia, e.g.…”

Section: Introductionmentioning

confidence: 99%

No evidence of predation causing female-biased sex ratios in marine pelagic copepods

Gusmão¹,

McKinnon²,

Richardson³

2013

Mar. Ecol. Prog. Ser.

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Although sex ratios close to unity are expected in dioecious species, biased sex ratios are common in nature. It is essential to understand causes of skewed sex ratios in situ, as they can lead to mate limitation and have implications for the success of natural populations. Femaleskewed sex ratios are commonly observed in copepods in situ. Here we discuss the challenges of copepod sex ratio research and provide a critical review of factors determining copepod sex ratios, focusing on 2 main objectives. The first is a critique of the male predation theory, which is currently the main process thought to be responsible for female-skewed sex ratios. It assumes that males have higher mortality because of increased vulnerability to predation during their search for mates. We show that there is little support for the male predation theory, that sex ratios skewed toward females occur in the absence of predation, that sex ratios are not related to predation pressure, and that where sex-skewed predation does occur, it is biased toward females. Our second objective is to suggest alternative hypotheses regarding the determination of sex ratios. We demonstrate that environmental factors, environmental sex determination and sex change have strong effects on copepod sex ratios, and suggest that differential physiological longevity of males and females may be more important in determining sex ratios than previously thought. We suggest that copepod sex ratios are the result of a mixture of factors.

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Sex ratios, intersexuality and sex change in copepods

Cited by 78 publications

References 56 publications

Does predation controls adult sex ratios and longevities in marine pelagic copepods?

Does predation controls adult sex ratios and longevities in marine pelagic copepods?

Optimal mate choice patterns in pelagic copepods

No evidence of predation causing female-biased sex ratios in marine pelagic copepods

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