Antagonistic selection on body size and sword length in a wild population of the swordtail fish, Xiphophorus multilineatus : Potential for intralocus tactical conflict

Alternative reproductive tactics (ARTs) have provided valuable insights into how sexual selection and life history tradeoffs can lead to variation within a sex. However, the possibility that tactics may constrain evolution through intralocus tactical conflict (IATC) is rarely considered. In addition, when IATC has been considered, the focus has often been on the genetic correlations between the ARTs, while evidence that the ARTs have different optima for associated traits and that at least one of the tactics is not at its optima is often missing. Here we investigate selection on three traits associated with the ARTs in the swordtail fish Xiphophorus multilineatus; body size, body shape and the sexually selected trait for which these fishes were named, sword length (elongation of the caudal fin). All three traits are tactically dimorphic, with courter males being larger, deeper bodied and having longer swords, and the sneaker males being smaller, more fusiform and having shorter swords. Using measures of reproductive success in a wild population we calculated selection differentials, linear and quadratic gradients, demonstrate that the tactics have different optima and at least one of the tactics is not at its optima for body size and sword length. Our results provide the first evidence of selection in the wild on the sword, an iconic trait for sexual selection. In addition, given the high probability that these traits are genetically correlated to some extent between the two tactics, our study suggests that IATC is constraining both body size and the sword from reaching their phenotypic optima. We discuss the importance of considering the role of IATC in the evolution of tactical dimorphism, how this conflict can be present despite tactical dimorphism, and how it is important to consider this conflict when explaining not only variation within a species but differences across species as well.

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Evidence for tactically antagonistic selection on body size and the sword in a wild population of the swordtail fish, Xiphophorus multilineatus

10.22541/au.160875615.53047765/v1 ◽

2020 ◽

Author(s):

Melissa Liotta ◽

Jessica Abbott ◽

Molly Morris ◽

Oscar Rios-Cardenas

Keyword(s):

Body Size ◽

Body Shape ◽

Behavioral Plasticity ◽

Wild Population ◽

Copulatory Behavior ◽

Alternative Reproductive Tactics ◽

Reproductive Tactics ◽

Genetic Conflict ◽

Antagonistic Selection ◽

Selection Gradients

Intralocus conflict has been well documented between the sexes, but much less is known about the potential for this genetic conflict in other polymorphisms, such as alternative reproductive tactics. Here we investigate two of three criteria necessary for demonstrating intralocus tactical conflict: the ARTs have different phenotypic optima for a shared trait, and one or both ARTs are not at their phenotypic optima for a shared trait. We address these two criteria in Xiphophorus multilineatus, a live-bearing freshwater fish that has two male alternative reproductive tactics, a behaviorally fixed courter male and a behaviorally plastic sneaker male that switches between courtship and force-copulatory behavior. We used measures of reproductive success from a wild population to estimate selection gradients on three tactically dimorphic traits involved in sexual selection: body size, body shape, and sword length. We present evidence that both body size and sword length are experiencing tactically antagonistic selection, providing evidence for both criteria. Additionally, selection on body shape in sneaker males appears to be buffered due to behavioral plasticity. Our study provides novel insight from a wild population into the role that intralocus tactical conflict can play in constraining ARTs from reaching their respective phenotypic optima despite tactical dimorphism.

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Body size, not age, predicts parasite load in Clark’s Spiny Lizards (Sceloporus clarkii)

Canadian Journal of Zoology ◽

10.1139/cjz-2017-0328 ◽

2019 ◽

Vol 97 (3) ◽

pp. 220-224 ◽

Cited By ~ 3

Author(s):

H.V. Watkins ◽

G. Blouin-Demers

Keyword(s):

Body Size ◽

Surface Area ◽

Intraspecific Variation ◽

Wild Population ◽

Parasite Load ◽

Older Individuals ◽

Fundamental Goal ◽

Males And Females ◽

Ectoparasite Load

Determining the factors that influence parasite load is a fundamental goal of parasitology. Body size often influences parasite load in reptiles, but it is unclear whether higher levels of parasitism are a result of greater surface area of individuals (a function of size) or of longer periods of exposure to parasites (a function of age). Using skeletochronology in a wild population of Clark’s Spiny Lizards (Sceloporus clarkii Baird and Girard, 1852), we tested the hypotheses that (i) larger individuals have higher parasite loads due to increased surface area available for colonization by parasites and their vectors and that (ii) older individuals have higher parasite loads because they have had longer exposure to parasites and their vectors. Males harboured more ectoparasites than females. Males and females differed in how body size influenced chigger (Acari: Trombiculidae) load; larger males harboured more chiggers than smaller males, but this was not the case in females. Age did not affect ectoparasite load in either sex. These results emphasize the importance of disentangling the effects of size and age in models of parasitism to gain a clearer understanding of intraspecific variation in parasite load.

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Outcome of dyadic conflict in male green swordtail fish, Xiphophorus helleri: Effects of body size and prior dominance

Animal Behaviour ◽

10.1016/s0003-3472(05)80842-5 ◽

1991 ◽

Vol 41 (3) ◽

pp. 417-424 ◽

Cited By ~ 78

Author(s):

Jacques Beaugrand ◽

Claude Goulet ◽

Daniel Payette

Keyword(s):

Body Size ◽

Xiphophorus Helleri ◽

Swordtail Fish ◽

Dyadic Conflict

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Conflict Outcome in Male Green Swordtail Fish Dyads (Xiphophorus Helleri): Interaction of Body Size, Prior Dominance/Subordination Experience, and Prior Residency

Behaviour ◽

10.1163/156853996x00161 ◽

1996 ◽

Vol 133 (3-4) ◽

pp. 303-319 ◽

Cited By ~ 84

Author(s):

Jacques P. Beaugrand ◽

Claude Goulet ◽

Daniel Payette

Keyword(s):

Body Size ◽

Prior Experience ◽

Social Experience ◽

The Other ◽

Xiphophorus Helleri ◽

Relative Contribution ◽

Large Size ◽

Swordtail Fish ◽

Prior Residency

AbstractThe relative contribution of asymmetries in prior experience, size, and prior residency to the determination of dyadic dominance between unacquainted individuals was examined using pairs of green swordtail fish, Xiphophorus helleri. Four types of encounters were staged between an intruder and a smaller resident: (1) both had experienced prior vicctory; (2) both had experienced prior defeat; (3) the intruder had experienced prior victory and the resident prior defeat; and (4) the intruder had experienced prior defeat and the resident prior victory. In a fifth condition in which two intruders met, one was a prior subordinate and the other a prior dominant smaller in size than its opponent. In all these encounters, the superiority in lateral surface of one fish varied between 0 to 30% over that of its opponent. Results showed that (1) when size differences between contestants were within the range of 0-10% and there was an asymmetry in prior social experience, conflicts were essentially resolved according to prior experience with prior winners systematically defeating prior losers; (2) prior residency of 3 h was an advantage only when both opponents had experienced prior defeat before meeting and when size asymmetries were small (e.g. < 20%). It was not an advantage between prior winners or between a prior winner and a prior loser; (3) when large size asymmetries existed (e.g. 20-30%), size uniquely determined dominance outcome and nullified other advantages or disadvantages due to prior social experience and prior residency; and (4) at intermediate levels of size asymmetries (e.g. 10-20%), size partially cancelled any advantage due to a prior victory, and gradually became paramount in accounting for victories.

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Quantitative inheritance of red eye pigment in Drosophila melanogaster

Genetics Research ◽

10.1017/s0016672300010016 ◽

1966 ◽

Vol 8 (2) ◽

pp. 143-164 ◽

Cited By ~ 5

Author(s):

Narendra S. Chauhan ◽

Forbes W. Robertson

Keyword(s):

Drosophila Melanogaster ◽

Body Size ◽

Wild Population ◽

Inbred Lines ◽

Pigment Content ◽

Phenotypic Variance ◽

Family Selection ◽

Genetic Determination ◽

Red Eye ◽

Selection For

1. The genetic and environmental variation of red eye pigment in individuals of a wild population of Drosophila melanogaster has been studied by extracting and measuring the pigment content of individual flies, which were also scored for eye and body size.2. Comparison of such variability in the wild population with the individual variation in crosses between inbred lines suggested that 60% of the phenotypic variance is genetic. About 75% of both genetic and environmental variance is due to intrinsic variation of pigment content while the remainder is correlated with eye size, which shows appreciable variation, independent of general body size, as measured by thorax length.3. Selection for high and low pigment content by both phenotypic and family selection led to 40–50% differences between high and low lines after eight genera tions. The response was asymmetrical and proceeded further and faster with selection for lower pigment content. Crosses between high and low lines showed positive departure from intermediacy, suggesting that more or less recessive effects had contributed to the selection for lower pigment content.4. There was some evidence of lower viability in the selected lines but no evidence of lower fertility or gamete viability in more extreme individuals of either sex.5. Comparison of pigment content, eye and body size at different temperatures and under different levels of crowding suggested that the pigment content per ommatidium is subject to a high degree of genetic determination.6. The average pigment content in strains derived from widely separated localities showed substantial variation, independent of both eye and body size.7. Inbred lines, derived from the same population, were found to differ greatly in pigment content. Crosses and the exchange of homologous pairs of chromosomes between two of these lines suggested that one or more completely recessive genes were fixed in both the second and third chromosome of one line, while the same second chromosome effect was also fixed in another line. The second and third chromosome difference reduced pigment content by respectively 30% and 50% and combined additively, judging by the effects of single and joint substitutions of homologous pairs.8. The possibility of combining genetic and biochemical analysis of pigment content is discussed.

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Evolutionary quantitative genetics of juvenile body size in a population of feral horses reveals sexually antagonistic selection

Evolutionary Ecology ◽

10.1007/s10682-019-09988-x ◽

2019 ◽

Vol 33 (4) ◽

pp. 567-584

Author(s):

Charlotte E. Regan ◽

Laura A. Tuke ◽

Julie Colpitts ◽

Philip D. McLoughlin ◽

Alastair J. Wilson ◽

...

Keyword(s):

Body Size ◽

Quantitative Genetics ◽

Feral Horses ◽

Antagonistic Selection ◽

Sexually Antagonistic Selection

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Female mimicry and an enhanced sexually selected trait: what does it take to fool a male?

Behaviour ◽

10.1163/000579510x519693 ◽

2010 ◽

Vol 147 (11) ◽

pp. 1443-1460 ◽

Cited By ~ 10

Author(s):

Molly Morris ◽

Abby Darrah ◽

Oscar Rios-Cardenas

Keyword(s):

Body Size ◽

Male Competition ◽

Alternative Mating Tactics ◽

Mating Tactics ◽

Pigment Pattern ◽

Swordtail Fish ◽

Female Mimicry

AbstractFemale mimicry is commonly considered in the context of alternative mating tactics as mimics can avoid male–male competition to gain increased access to females. We describe a case where one of the benefits to being a female mimic could be the increase in size of a sexually selected trait that should eventually decrease the mimics' ability to fool males. In the swordtail fish Xiphophorus nezahualcoyotl, a small percentage of males have a permanent pigment pattern known as 'false brood spot' (FBS), express a horizontal bar pigment pattern common for females, and yet have longer swords (a sexually selected trait) for their body size. FBS males did not use more 'coercive' behaviours in the field, and females do not appear to distinguish between males based on whether or not they have FBS in the laboratory. However, in the field males with FBS were chased less by other males, spent significantly more time feeding, and those that expressed the horizontal bar had greater access to females. We suggest that FBS males with swords can still fool other males into thinking they are females because the true brood spot remains informative as long as the frequency of FBS males (mimics) remains low.

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