Samuel Cotton’s research while affiliated with University College London and other places

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Publications (27)


Figure 1: Map showing the 12 sites used for collections and the University of Malaya Field Studies Centre. All sites represent distinct populations that lie along or near to the small Gombak road, Jalan Gombak, which runs through mountainous rainforest. To the upper left is a major motorway in the valley. In addition to the rainforest, the map also shows the local quarry (bottom centre left). A compass is shown for orientation and the bar on the bottom left indicates a scale of 1000 m. Google Earth Image © 2013 DigitalGlobe © 2013 MapIt.
Table 1 Relationships between X-linked microsatellite loci and phenotypic traits
Figure 2: Frequency distribution of the proportion of female offspring in each brood for flies collected in 2009 and 2011 (N=134). Dark grey bars indicate sex ratios that differ significantly from 1:1.
Figure 3: Association between sex ratio, given by the proportion of females in the brood, and ms395 allele size given in 10 bp groupings. The line joins adjacent mean values. A significant relationship was found, with larger ms395 alleles associated with more female-biased broods.
Figure 4: Box plot (Q1, median, Q3) of ms395 allele sizes found at 12 sites along the Gombak valley (see for locations). Whiskers (Q1−1.5*interquartile range (IQR), Q3+1.5*IQR) show the spread of the allele sizes and outliers (mainly large alleles). Six of the 12 sites (circled) show the presence of large ms395 alleles (>218 bp), whereas the other six sites show a complete absence of large alleles.
Male eyespan size is associated with meiotic drive in wild stalk-eyed flies (Teleopsis dalmanni)
  • Article
  • Full-text available

April 2014

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464 Reads

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42 Citations

Heredity

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S Cotton

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This study provides the first direct evidence from wild populations of stalk-eyed flies to support the hypothesis that male eyespan is a signal of meiotic drive. Several stalk-eyed fly species are known to exhibit X-linked meiotic drive. A recent quantitative trait locus analysis in Teleopsis dalmanni found a potential link between variation in male eyespan, a sexually selected ornamental trait, and the presence of meiotic drive. This was based on laboratory populations subject to artificial selection for male eyespan. In this study, we examined the association between microsatellite markers and levels of sex ratio bias (meiotic drive) in 12 wild T. dalmanni populations. We collected two data sets: (a) brood sex ratios of wild-caught males mated to standard laboratory females and (b) variation in a range of phenotypic traits associated with reproductive success of wild-caught males and females. In each case, we typed individuals for eight X-linked microsatellite markers, including several that previously were shown to be associated with male eyespan and meiotic drive. We found that one microsatellite marker was very strongly associated with meiotic drive, whereas a second showed a weaker association. We also found that, using both independent data sets, meiotic drive was strongly associated with male eyespan, with smaller eyespan males being associated with more female-biased broods. These results suggest that mate preference for exaggerated male eyespan allows females to avoid mating with males carrying the meiotic drive gene and is thus a potential mechanism for the maintenance and evolution of female mate preference.Heredity advance online publication, 8 January 2014; doi:10.1038/hdy.2013.131.

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Table 1 Examination of multiple signals used in mate choice 
Figure 2 Frequency distribution of P Field , the preference function of wild males. P Field accounts for the harem size, the number of large and small females available, and the dynamic changes in these variables between matings. P Field = 0 indicates no preference, P Field < 0 indicates a preference for small eyespan females, and P Field > 0 indicates a preference for large eyespan females. 
Figure 3 Frequency distribution of P Lab , the preference function of laboratory males, when given the choice of mating with either a large or small female. In the laboratory assays, there is no dynamic change in the number of females available because females cannot leave the test arena. For P Lab , P = 0 indicates no preference, P Lab < 0 indicates a preference for small eyespan females, and P Lab > 0 indicates a preference for large eyespan females. 
Figure 4 The effect of fecundity on male mate preference (independent of eyespan). Male mate preference for large eyespan females (P Lab ), when females were fed a high-quality diet and had high fecundity (treatment one) or a reduced diet and had low fecundity (treatment 2). There was stronger male mate preference when females were on the high-quality diet. The line represents the mean preference of the 2 diet treatments. *P < 0.05. 
Male mate preference for female eyespan and fecundity in the stalk-eyed fly, Teleopsis dalmanni

March 2014

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268 Reads

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35 Citations

Behavioral Ecology

Traditional views of sexual selection view males as the indiscriminate sex, competing for access to choosy females. It is increasingly recognized that mating can also be costly for males and they are therefore likely to exhibit choice in order to maximize their reproductive success. Stalk-eyed flies are model species in sexual selection studies. Males are sperm limited and constrained in the number of matings they are able to partake in. In addition, variation in female fecundity has been shown to correlate positively with female eyespan, so eyespan size could provide males with a reliable signal of female reproductive value. We examined male mate preference in the wild in the stalk-eyed fly, Teleopsis dalmanni. In addition, we set up experiments in the laboratory allowing males a choice between females that varied in 1) eyespan (a proxy for fecundity) and/or 2) fecundity (manipulated through diet). We found that males exhibited preference for large eyespan females, both in the wild and laboratory studies. As well as using female eyespan as a mating cue, males were also able to assess female fecundity directly. Changes in fecundity among large eyespan females caused corresponding changes in male mate preference, whereas changes in the fecundity of small eyespan females had limited effect on their attractiveness. These results show that male mate preferences are a prevalent feature of a canonical example of female mate choice sexual selection and that males use multiple cues when they assess females as potential mates.


Figure 2. Changes in fecundity (A), absolute fertility (B) relative fertility (C) and percentage fertility (D) over time in captivity for females that received a single additional mating (shaded bars) or an interrupted mating (open bars). Time periods that are not connected by the same letter are significantly different (Tukey HSD comparison of pooled (mated plus interrupted) means). Data displayed as least squares means 6 SE. doi:10.1371/journal.pone.0014309.g002 
Data displayed as least squares means ± SE.
Time periods that are not connected by the same letter are significantly different (Tukey HSD comparison of pooled (mated plus interrupted) means). Data displayed as least squares means ± SE.
No Detectable Fertility Benefit from a Single Additional Mating in Wild Stalk-Eyed Flies

December 2010

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56 Reads

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9 Citations

Multiple mating by female insects is widespread, and the explanation(s) for repeated mating by females has been the subject of much discussion. Females may profit from mating multiply through direct material benefits that increase their own reproductive output, or indirect genetic benefits that increase offspring fitness. One particular direct benefit that has attracted significant attention is that of fertility assurance, as females often need to mate multiply to achieve high fertility. This hypothesis has never been tested in a wild insect population. Female Malaysian stalk-eyed flies (Teleopsis dalmanni) mate repeatedly during their lifetime, and have been shown to be sperm limited under both laboratory and field conditions. Here we ask whether receiving an additional mating alleviates sperm limitation in wild females. In our experiment one group of females received a single additional mating, while a control group received an interrupted, and therefore unsuccessful, mating. Females that received an additional mating did not lay more fertilised eggs in total, nor did they lay proportionately more fertilised eggs. Female fertility declined significantly through time, demonstrating that females were sperm limited. However, receipt of an additional mating did not significantly alter the rate of this decline. Our data suggest that the fertility consequences of a single additional mating were small. We discuss this effect (or lack thereof), and suggest that it is likely to be attributed to small ejaculate size, a high proportion of failed copulations, and the presence of X-linked meiotic drive in this species.


Male Mutation Bias and Possible Long‐Term Effects of Human Activities

October 2010

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30 Reads

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9 Citations

The ability of a population to adapt to changing environments depends critically on the amount and kind of genetic variability it possesses. Mutations are an important source of new genetic variability and may lead to new adaptations, especially if the population size is large. Mutation rates are extremely variable between and within species, and males usually have higher mutation rates as a result of elevated rates of male germ cell division. This male bias affects the overall mutation rate. We examined the factors that influence male mutation bias, and focused on the effects of classical life-history parameters, such as the average age at reproduction and elevated rates of sperm production in response to sexual selection and sperm competition. We argue that human-induced changes in age at reproduction or in sexual selection will affect male mutation biases and hence overall mutation rates. Depending on the effective population size, these changes are likely to influence the long-term persistence of a population.


Figure 1. Median number of aggressive interactions AE interquartile range across all male eyespan pairs for (a) the laboratory experiment (N ¼ 160: equal sample sizes) and (b) the field data (N ¼ 37: LL: N ¼ 6; LS: N ¼ 11; SL: N ¼ 3; SS: N ¼ 17). Asterisks denote the group with a significant difference (*** P < 0.001). See text for details of pairs. 
Small J, Cotton S, Fowler K, Pomiankowski A.. Male eyespan and resource ownership affect contest outcome in the stalk-eyed fly, Teleopsis dalmanni. Anim Behav 78: 1213-1220

November 2009

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290 Reads

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47 Citations

Animal Behaviour

The dominant theory for the evolution of male sexual ornaments is that they act as signals of male quality used by females in their mate choice. But these traits may also be used in male–male competition. In stalk-eyed flies, male eyespan (the distance between the eyes) is already known to play an important role in female mate choice. We investigated the influence of eyespan on male aggression over control of lek mating sites, both under controlled conditions and from field observations. Eyespan positively affected the number of aggressive encounters between two males on a lek. There were more aggressive interactions between large-eyespan males compared with small-eyespan males, and large-eyespan males won proportionately more aggressive interactions. Lek site ownership also influenced the outcome of aggression but to a smaller degree than eyespan. In addition, higher resource value, the number of females on a lek, increased the chance of aggression. The outcome of aggression between males is the control of lek aggregation sites, and this had direct consequences for male reproductive success, as lek owners gained more matings at both dusk and dawn. The importance of male–male competition in shaping sexual selection in stalk-eyed flies is discussed.


Condition-dependent mutation rates and sexual selection

February 2009

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17 Reads

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12 Citations

Journal of Evolutionary Biology

'Good genes' models of sexual selection show that females can gain indirect benefits for their offspring if male ornaments are condition-dependent signals of genetic quality. Recurrent deleterious mutation is viewed as a major contributor to variance in genetic quality, and previous theoretical treatments of 'good genes' processes have assumed that the influx of new mutations is constant. I propose that this assumption is too simplistic, and that mutation rates vary in ways that are important for sexual selection. Recent data have shown that individuals in poor condition can have higher mutation rates, and I argue that if both male sexual ornaments and mutation rates are condition-dependent, then females can use male ornamentation to evaluate their mate's mutation rate. As most mutations are deleterious, females benefit from choosing well-ornamented mates, as they are less likely to contribute germline-derived mutations to offspring. I discuss some of the evolutionary ramifications of condition-dependent mutation rates and sexual selection.


Table 2 The effect of eyespan on variation in reproductive quality in females
Eyespan reflects reproductive quality in wild stalk-eyed flies

January 2009

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361 Reads

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50 Citations

Evolutionary Ecology

Handicap models of sexual selection propose that females use male sexual ornaments as a cue in mate choice because they reflect commodities that increase female fitness, either directly or indirectly. In contrast to studies on vertebrates, most investigations of ornaments in insects and other invertebrate taxa have been conducted under laboratory conditions. There is a pressing need to address questions relating to sexual signalling of quality in natural populations, as the arbitrary and uniform environments found in the laboratory fail to reflect the world under which animals have evolved. We investigated associations between male ornaments (exaggerated eyespan), attractiveness, and reproductive quality in a wild population of the sexually ornamented stalk-eyed fly, Teleopsis dalmanni. We also explored the relationship between eyespan and reproductive quality in females to evaluate the potential for sexually antagonistic selection on eyespan. We show that eyespan is a generic correlate of reproductive quality, acting as a reliable mirror of variation in reproductive fitness in both sexes. Our findings suggest that male ornaments signal commodities that are of interest to females in the natural environment in which they, and mate preferences for them, have evolved. In addition, the covariance between female eyespan and reproductive output suggests that the former may be a reliable cue of quality in its own right. Our data provide important insights into the evolutionary forces that shape the evolution of exaggerated eyespan in wild populations of this species.


Population Consequences of Environmental Sex Reversal

October 2008

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92 Reads

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90 Citations

When sex determination in a species is predominantly genetic but environmentally reversible, exposure to (anthropogenic) changes in the environment can lead to shifts in a population's sex ratio. Such scenarios may be common in many fishes and amphibians, yet their ramifications remain largely unexplored. We used a simple model to study the (short-term) population consequences of environmental sex reversal (ESR). We examined the effects on sex ratios, sex chromosome frequencies, and population growth and persistence after exposure to environmental forces with feminizing or masculinizing tendencies. When environmental feminization was strong, X chromosomes were driven to extinction. Analogously, extinction of normally male-linked genetic factors (e.g., Y chromosomes) was caused by continuous environmental masculinization. Although moderate feminization was beneficial for population growth in the absence of large viability effects, our results suggest that the consequences of ESR are generally negative in terms of population size and the persistence of sex chromosomes. Extreme sex ratios resulting from high rates of ESR also reduced effective population sizes considerably. This may limit any evolutionary response to the deleterious effects of ESR. Our findings suggest that ESR changes population growth and sex ratios in some counter-intuitive ways and can change the predominant factor in sex determination from genetic to fully environmental, often within only a few tens of generations. Populations that lose genetic sex determination may quickly go extinct if the environmental forces that cause sex reversal cease.


Individual recognition: mice, MUPs and the MHC

December 2007

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22 Reads

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6 Citations

Current Biology

Recognition requires that identity be assigned to specific individuals as a result of perceived differences in their unique features and attributes. A recent study demonstrates that this phenomenon occurs in mice, and reveals the genetic signal that underlies it.


Introduction of Trojan sex chromosomes to boost population growth

December 2007

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75 Reads

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33 Citations

Journal of Theoretical Biology

Conservation programs that deal with small or declining populations often aim at a rapid increase of population size to above-critical levels in order to avoid the negative effects of demographic stochasticity and genetic problems like inbreeding depression, fixation of deleterious alleles, or a general loss of genetic variability and hence of evolutionary potential. In some situations, population growth is determined by the number of females available for reproduction, and manipulation of family sex ratios towards more daughters has beneficial effects. If sex determination is predominantly genetic but environmentally reversible, as is the case in many amphibia, reptiles, and fish, Trojan sex chromosomes could be introduced into populations in order to change sex ratios towards more females. We analyse the possible consequences for the introduction of XX-males (XX individuals that have been changed to phenotypic males in a XY/XX sex determination system) and ZW males, WW males, or WW females (in a ZZ/ZW sex determination system). We find that the introduction of WW individuals can be most effective for an increase of population growth, especially if the induced sex change has little or no effect on viability.


Citations (25)


... Nearly all species of Diopsidae (Bilberg, 1820) are well-known for their exaggerated eye stalks (Shillito 1971). There are approximately 160-8000 species and 10-15 genera containing stalk-eyed flies in the family Diopsidae (Shillito 1971;Steyskal 1972;Carr et al. 2006;Ovtshinnikova and Galinskaya 2016;Roskov et al. 2019). Although both males and females in Diopsinae have eyes that are laterally displaced from the central head, the level of sexual dimorphism varies between and within species (Burkhardt and de la Motte 1985; Wilkinson and Dodson 1997;Meier and Hilger 2000). ...

Reference:

Description of the karyotype of Sphyracephala detrahens (Diptera, Diopsidae)
A description of a new species of Diasemopsis (Diptera, Diopsidae) from the Comoro Islands with morphological, molecular and allometric data

Zootaxa

... The geographically close habitat ranges of Bactrocera and the potential donor genus Teleopsis led to the proposal that the horizontal transfer may have occurred in New Guinea. The species composition of Teleopsis is under debate [29][30][31], however here it is used within its broadest sense to include the putatively nested or synonymous genera Cyrtodiopsis and Megalobops. ...

A morphological and molecular description of a new Teleopsis species (Diptera: Diopsidae) from Thailand
  • Citing Article
  • October 2007

Zootaxa

... It has long been recognized that the genetic relationship between male sexual display traits and components of nonsexual fitness such as condition is an important empirical pursuit in understanding the evolution of female mating preferences (Cotton et al., 2004;Hunt et al., 2004;Tomkins et al., 2004). Our results suggest that if we are to understand the evolution of male mating preferences, analyses of male preferences for female sexual display traits will need to be complemented with a detailed understanding of their genetic basis. ...

Do insect sexual ornaments demonstrate heightened condition dependence?
  • Citing Article
  • September 2005

... Although less studied than female mate choice, there is evidence that male mate choice is common across taxa [15][16][17][18][19] and is often based on female traits that are correlated with fecundity [17][18][19][20][21]. Despite reproductive senescence causing female fecundity to decline with age, there is mixed evidence of how male mate choice is affected by female age. ...

Male mate preference for female eyespan and fecundity in the stalk-eyed fly, Teleopsis dalmanni

Behavioral Ecology

... Females have evolved responses or preferences to prevent them from mating with SGE carriers in some cases. In stalk-eyed flies, females preferentially mate with males with wider eye spans, whereas SGE-carrying males are generally associated with smaller eye spans (Cotton et al., 2014;Wilkinson et al., 1988). The presence of sperm-killing meiotic drive also correlates with the rate of polyandry in populations, where meiotic drive is more common in areas with low polyandry (Pinzone & Dyer, 2013;Price et al., 2014). ...

Male eyespan size is associated with meiotic drive in wild stalk-eyed flies (Teleopsis dalmanni)

Heredity

... Chaetodiopsis Séguy (Diopsinae). An endemic genus of two described species: C. comoroensis (Carr & Földvári, 2006), described from Comoros (Carr et al. 2006); and C. meigenii, the commonest sub-Saharan diopsid, widely distributed in the continental Afrotropics and even extending into Oman in the Southern Arabian Peninsula . The genus is one of the four genera comprising the Diasemopsis genus-group. ...

A Description Of A New Species Of Diasemopsis (Diptera, Diopsidae) From The Comoro Islands With Morphological, Molecular And Allometric Data

Zootaxa

... Common ancestry makes species means nonindependent of each other (Felsenstein, 1985); thus, we also performed the same sets of analyses described above with phylogeny taken into account. Because there is no published phylogeny that includes all of the taxa we studied, we created a composite phylogeny (Fig. 1) from Baker & Wilkinson (2001), Wright et al. (2004), Swallow et al. (2005), and Földvári et al. (2007, and set branch lengths equal to 1 because the divergence times among the different species are unclear. We then used the PDAP:PDTREE module (Garland, Midford & Ives, 1999; Midford, Garland & Maddison, 2005) in MESQUITE, version 2.72 (Maddison & Maddison, 2009) to calculate standardized phylogenetically independent contrasts (Felsenstein, 1985). ...

A morphological and molecular description of a new Teleopsis species (Diptera: Diopsidae) from Thailand

Zootaxa

... Biological ornaments are conspicuous traits considered to function as condition-dependent signals of mate quality during mate selection (Hill, 2014;Winters, 2018), though they may serve a dual role as armaments (i.e., weapons or status badges; Berglund et al., 1996). Examples of visual ornamentation can be found across many taxa, such as the colourful iridescent tail feathers of peacocks (Pavo cristatus; Dakin and Montgomerie, 2013) and the long eye stalks of stalk-eyed flies (Teleopsis dalmanni; Cotton et al., 2010). As condition-dependent signals, ornaments are reported to have higher quality under more favourable environmental conditions (e.g., head ornaments of unparasitised vs parasitised male red jungle fowl, Gallus gallus, progenitor of the domestic fowl; Zuk et al., 1990). ...

Eyespan reflects reproductive quality in wild stalk-eyed flies

Evolutionary Ecology

... This may also explain why the relationship between the vibrational interaction and frontal leg length found for losers have similar but non-significant trends as the ones found for winners. In animal contests, it is common for the larger rival to be more aggressive than the smaller one (e.g. Brown et al. 2006;Small et al. 2009;Graham et al. 2020) including spider contests (Whitehouse 1997;Taylor et al. 2001;Elias et al. 2008). In T. clavipes, in particular, males escalate the interaction to physical contact more frequently when the contest involves two individuals of greater size than two individuals of smaller size (Constant et al. 2011). ...

Small J, Cotton S, Fowler K, Pomiankowski A.. Male eyespan and resource ownership affect contest outcome in the stalk-eyed fly, Teleopsis dalmanni. Anim Behav 78: 1213-1220

Animal Behaviour

... The direct benefits and costs of polyandry have been documented for several species of insects, even when only using two males as the polyandry treatment Wedell 1998, Worthington andKelly 2016). Nonetheless, in other cases, the direct benefits of polyandry are not detected or are minimal (Jennions et al. 2007, Harley et al. 2010, as in this experiment. Regarding the possible indirect benefits of polyandry beyond egg viability, like inbreeding avoidance, increased genetic compatibility, and increased offspring fitness (Ivy and Sakaluk 2005) it was not possible to detect them with our design, and requires further scrutiny (Jennions et al. 2007, Slatyer et al. 2012. ...

No Detectable Fertility Benefit from a Single Additional Mating in Wild Stalk-Eyed Flies