EXTRA VIEW Fly 6:1, 3–11; January/February/March 2012; G 2012 Landes Bioscience

The of multiple mating Costs and benefits of polyandry to females and of polygyny to males

Patricia Adair Gowaty Department of Ecology and Evolutionary ; Institute of Environment and Sustainability; UCLA; Los Angeles, CA USA; Smithsonian Tropical Research Institute; Washington, DC USA; Polistes Foundation, Inc.; Belmont, MA USA View metadata, citation and similar papers at core.ac.uk brought to you by CORE

provided by PubMed Central olyandry is a paradox: why do opportunities and constraints mold P females mate multiple times when evolutionary responses. a single ejaculate often provides enough sperm for lifetime egg production? Gowaty et al. addressed explanations for Multiple Mating in Drosophila polyandry in Drosophila pseudoobscura from the perspective of hypotheses based “Multiple mating” is mating with more © 2012 Landeson sex differences in costs of reproduction Bioscience.than one potential mate, which potentially (CoR). Contrary to CoR, Gowaty et al. produces offspring of mixed parentage. showed that (1) a single ejaculate was Multiple mating is called “polyandry” inadequate for lifetime egg production; when females do it and “polygyny” when (2) polyandry provided fitness benefits to males do it. In the vast majority of tested females beyond provision of adequate species, females mated in nature produce Do notsperm and (3)distribute. fitness benefits of poly- offspring sired by more than one male. andry were not offset by costs. Here, I Polyandry is common in wild Droso- discuss predictions of the ad hoc hypo- phila,1-17 but also in crickets,18 burying theses of CoR and three alternative beetles19 and other insects,20 as well as hypotheses to CoR to facilitate a discus- birds21 and mammals.22,23 Compared with sion and further development of a strong birds, in which studies of hundreds of inference approach to experiments on the species in the wild demonstrate the adaptive significance of polyandry for ecological correlates of genetic polyandry, females. Each of the hypotheses makes generalities about Drosophila polyandry Keywords: multiple insemination, cost of testable predictions; simultaneous tests of come mostly from laboratory studies, and reproduction, compensation hypothesis, the predictions will provide a strong most generalities about Drosophila poly- mating theory, switch point theorem, inference approach to understanding the andry come from only two species, sexual conflict adaptive significance of multiple mating. D. melanogaster and D. pseudoobscura, I describe a sex-symmetric experiment though this is changing as more behavioral Submitted: 09/01/11 meant to evaluate variation in fitness and evolutionary ecologists24 ask questions Revised: 10/05/11 among lifelong virgins (V); monogamous about non-model Drosophila and Accepted: 10/05/11 females and males with one copulation Drosophila species in nature. Despite (MOC); monogamous females and males enormous success in understanding the http://dx.doi.org/10.4161/fly.18330 with multiple copulations (MMC); PAND, ecology of polyandry in birds and its costs Correspondence to: Patricia Adair Gowaty; polyandrous females; and PGYN, polygyn- and benefits to wild-living females, much Email: [email protected] ous males. Last, I recommend the study less is known about proximate causation in of many different species, while taking birds than in Drosophila. Almost all we Extra View to: Gowaty PA, Kim YK, Rawlings J, ’ Anderson WW. Polyandry increases offspring care in choice of study species and now know of polyandry s proximate causes viability and mother productivity but does not attention to the assumptions of specific has come from Drosophila. A better decrease mother survival in Drosophila hypotheses. I particularly urge the study understanding of the ultimate causes pseudoobscura. Proc Natl Acad Sci USA 2010; of many more Drosophila species both in of polyandry in a variety of species of 107:13771–6; PMID:20643932; http://dx.doi.org/ laboratory and the wild to understand Drosophila, along with more studies of 10.1073/pnas.1006174107 the “nature of flies in nature,” where Drosophila in the wild, will close the

www.landesbioscience.com Fly 3 intertwining linkages of proximate and the laboratory, male Drosophila multiple In this paper, I describe conceptual and ultimate causation in the paradoxes of mating is much easier to observe, espe- theoretical ideas (Table 1) that together polyandry—at least for Drosophila—and cially under experimental mating schemes allow a strong inference33 approach to provide additional direction for studies of with sequential presentations of females current investigations of the costs and polyandry in other taxa. to subject males; and, in the laboratory, benefits to polyandry in species from any In laboratory studies of multiple male multiple mating is common.13 taxa, concentrating on the implications in Drosophila species, females often readily Observations in some species suggest studies of Drosophila. The ideas that I mate with more than one male.15,17,25 that female re-mating rate may be higher consider here have implications for future Investigators often present experimental than male re-mating rate,28 which may investigations of the fitness consequences males to females sequentially rather than be associated with sex differences in for both females and males of multiple simultaneously, and this methodology has development time, in turn affecting the mating, i.e., of genetic polyandry and led to categorization of species as those operational sex ratio at eclosion sites genetic polygyny. I also suggest an experi- with females re-mating at relatively fast where females often commence mating.17 ment for the future (Table 2), from the vs. slow rates.17 There are very few fly Even Bateman’s29 classic laboratory experi- perspective of a balanced approach34 to the species in which most females mate just ment with D. melanogaster suggested on constraints and opportunities for males31,35 once.17,26,27 In contrast, no studies of reflection30,31 and later re-analysis32 that and females of multiple mating. Drosophila from nature have demon- most females re-mated more than once, strated that specific males have sired sometimes as often as most males in the Polyandry Hypotheses offspring with more than one female, experimental trials. Thus, the widespread which might be explained by the metho- general expectation derived mostly from Hypotheses 1–5: Cost of reproduction. dological difficulty of assigning rather than laboratory studies of D. melanogaster Anisogamy36 and parental investment37 rejecting paternity (assigning paternity is a that male Drosophila always re-mate theories are evolutionary explanations for ©problem not2012 unique to Drosophila, butLandesmore often than females re-mate Bioscience. remains fixed sex differences in pre-copulatory and also in studies of other wild animals). In speculation. copulatory mating behavior and physi-

Table 1. Comparison of fitness predictions for scenarios from cost of mating, compensation, demographic stochastic mating theory and the switch point theorem Component of Fitness PolyandryDo notNumber of distribute.Egg to adult Number adult Mother Adult offspring hypotheses fertile eggs survival† offspring survival* survival†

MOC MMC PM MOC MMC PM MOC MMC PM MOC MMC PM MOC MMC PM

1 1 CoR: Guards against “sperm limitation” MOC , MMC =PM No prediction No prediction No prediction No prediction

1,2 2 CoR: Decreases gamete incompatibilities MOC =MMC , PM No prediction No prediction No prediction No prediction

1 3 CoR: Enhances offspring health MOC =MMC , PM MOC =MMC , PM MOC =MMC , PM No prediction MOC =MMC , PM

1 4 CoR: Enhances direct benefits to females No prediction No prediction No prediction MOC # MMC # PM No prediction

1,2 5 CoR: Male coercion of remating by MOC =MMC =PM MOC =MMC =PM MOC =MMC =PM MO $ MMC $ PM MOC =MMC =PM females

3 6 Compensation MOC =MMC , PM MOC =MMC , PM MOC =MMC , PM MO $ MMC $ PM MOC =MMC , PM

4 7 Demographic stochastic mating theory MOC # MMC , PM No prediction ## No prediction No prediction

5 8 Switch Point Theorem MOC =MMC , PM MOC =MMC , PM MOC =MMC , PM MOC =MMC =PM MOC =MMC , PM Hypotheses for polyandry predict differences in components of fitness and the direction of effect comparing experimental treatments. The experimental treatments are (1) females with access to one randomly assigned male during only one day of their lives, i.e., monogamous females with one copulation MOC; (2) females with continuous access to a single randomly assigned male; i.e., monogamous females with multiple copulations MMC and (3) polyandrous females with access to a different randomly-assigned male (controlling for age and experience of males in MMC) on each day of the experiment; i.e., polyandrous females with multiple copulations, PMC. Read the entries thusly: MOC = MMC = PMC and so forth. *Mother survival is always expected to be lower for mothers with greater contact with conspecifics as required when females mate with more than one male, because of higher risk to pathogens and parasites, unless pathogen risk is offset by greater access to resources or other factors. †Offspring survival/per cohort is almost always expected to be higher under hetorozygosity, particularly at immune coding loci, which in many ecological circumstances will be higher when mothers have broods sired by more than one male. 1Assumes the cost of reproduction CoR organizes sex differences, and for species in which eggs are larger than sperm, assumes females are choosy about mating, but males indiscriminate; assumptions and predictions are sex-asymmetric, differing for males and females. 2CoR assumptions plus assume males are not just indiscriminate but coerce females into mating; and there are no additional benefits of multiple mating over single mating for females; asymmetric expectations for females and males. 3Compensation assumes that offspring viability determines mate preferences, constraints on mating with one’s most preferred exist and that under constraints individuals will attempt to compensate for offspring viability deficits. 4Assumes demographic stochasticity affects opportunities for mating and all mating is “on encounter” (i.e., indiscriminate); symmetric expectations for females and males. 5Assumes individual time available for mating and the likelihood of fitness conferred or lost from a particular mating determine whether an individual “accepts” a potential mate on encounter (is “indiscriminate”)or“rejects” an encountered potential mate and waits for a partner with whom the individual will have higher fitness offspring (is “choosy”).

4 Fly Volume 6 Issue 1 Table 2. The design of a sex-symmetric experiment to evaluate the costs and benefits of multiple mating Treatments (A through H) Alone adults Monogamy varied copulations Multiple mating Female Male Single copulation Many copulations Life-time Female Male One-day exposure to exposure to the same “Polyandry” “Polygyny” partner partner New virgin New sexually New virgin *New sexually male daily experienced male daily female daily experienced female daily AB C D E F G H

With these treatments we will test the following predictions: (1) Assuming that the metabolic cost of producing eggs is greater than producing sperm, virgin females (A) die before virgin males (B). (2) Assuming that the cost to mating is greater in females than males, males live longer than females (D males . females). (3) Assuming that mating is costly, mated females die before virgin females (C females . A) and mated males die before virgin males (C males . B). (4) Assuming that female reproduction is limited by access to sperm, monogamous females who copulate once (C) lay fewer viable eggs than monogamous females who copulate repeatedly (D). (5) Assuming that polyandrous females have access to more variation in male haplotypes compared with monogamous females with constant access to males (D - while controlling variation in male age and experience), polyandrous females (F) have healthier offspring (% egg-to-adult-survival), more offspring who survive to eclosion and more adult offspring who survive longer. (6) Assuming that male quality varies with mating status, polyandrous females mated to a new virgin male every day (E) will lay more eggs than polyandrous females mated to sexually experienced males (F). (7) Assuming that multiple mating is associated with access to females with different alleles at immune coding loci, polygynous males (G) have healthier offspring than monogamous males – not controlling for female experience between treatments because males get a new virgin female everyday D males. (8) Assuming polygyny is costly for males, G and H males will die before D males. (9) Assuming that multiple mating is associated with access to more alleles at immune coding loci, polygynous males (H) have healthier offspring than monogamous males (D) while controlling between treatments for female age and mating experience, i.e., D , H. (10) Assuming pathogen risk is greater for polygynous than monogamous males, polygynous males (H) will die sooner ©than monogamous 2012 males (D) while controlling betweenLandes treatments for female age and mating Bioscience. experience, i.e., D . H. ology of males and females. Both aniso- could be attempts to persuade reluctant no survival differences between mono- gamy and parental investment assume that females to mate, or it could be, as it is in gamous and polyandrous females, one reproduction extracts predictable, deter- many bird and mammal species, a mech- must seek other explanations for sex ministic costs that are greater in females anistic way to coordinate male and female differences in mating behavior. Yet, only than males, and thereby, in most species reproductive hormones; or it could be a a very few investigators have considered favoring choosy femalesDo and indiscriminate nottype of communication distribute. serving collabora- that non-confirmatory empirical observa- males. I call these arguments collectively tive functions between females and males tions are actually a challenge to CoR ideas. “scenarios from the cost of reproduction” both of whom have already indicated that Confronted with empirical inconsistency, (CoR). CoR assumes the above selection the other is an acceptable mate. Instead of many investigators instead cast ad hoc arguments and predicts that selection acts evaluating these alternatives, most investi- hypotheses of, e.g., “requisite” sexual con- differently on females and males such that gators simply proclaim the generality of flict from the “coy female, ardent male” male mating rate is much higher than Darwin’s observations, Bateman’s conclu- imperative to explain contrary data. In female mating rate. sions41 and CoR’s predictions. Thus, they addition to evidence inconsistent with CoR arguments provide conceptual expect the optimal mating frequency for CoR, many criticisms of the CoR assump- backing for Darwin’s38 observations and females to be once or always less than tions exist: it is unsurprising that there Bateman’s29 “principles” that (1) females males, particularly in species in which are many ad hoc adjustments to the basic are choosy and males indiscriminate about females store sperm. Under CoR assump- CoR assumptions. mating (2) which causes male variance in tions, it is unlikely that mating with more There are five CoR polyandry hypo- number of mates to be greater than female than one male increases female reproduct- theses (Table 1) with predictions about variance in number of mates so that (3) ive success. CoR scenarios predict that the benefits and costs of polyandry. The number of mates has a stronger effect on males provide to females in a single predictions vary depending on additional male reproductive success than female ejaculate enough sperm to fertilize their assumptions about what fitness benefits to reproductive success. entire lifetime of egg production. And, females, either direct or indirect, organize Many investigators assume the veracity under most characterizations of CoR female choices of mates. For example, if of the CoR arguments about choosy assumptions, but not all,35 whenever female mate choice only guards against females and ardent males; yet very few CoR is lower for males than females, sperm limitations (hypothesis 1), such as experiments exist39,40 that were designed to males are predicted to be ardent and insufficient or defective sperm or incom- test under experimentally controlled con- enthusiastic about mating, while females patibilities between gametes (hypothesis ditions for the existence and magnitude of are predicted to be retiring, coy, relatively 2), the hypothesis predicts that the num- sex differences in pre-mating behavior. passive and choosy about mating. ber of eggs laid is less for females who Nor, are there studies that evaluate the Observations inconsistent with CoR. copulate one time rather than multiple many alternative hypotheses, for what is On the face of it, the very existence of times, independent of whether the mul- called “courtship” by males; “courtship” polyandry rejects CoR. When there are tiple copulations are with the same male.

www.landesbioscience.com Fly 5 Discerning between hypothesis 1 and effects on the evolution of both female which supportive data exist.60,61 Why not hypothesis 2 when there is empirical and male traits. imagine that the dynamic interactions and consistency with their predictions requires The “male coercion of females” sexual their outcomes between females and males additional mechanistic studies to evaluate conflict hypothesis (hypothesis 5) predicts lead sometimes to reversals of power the cause(s) of variation in egg number. (Table 1) that egg-to-adult survival, num- between the sexes, and over time, to sex- If one assumes that females choose ber of adult offspring, and survival of symmetric power distributions?49 Why not mates for enhanced offspring health bene- adult offspring will be statistically similar imagine a dance of symmetric jousting fits, (hypothesis 3) the CoR predicts whether females mate monogamously or over the, only sometimes, competing, but higher number of eggs laid, higher egg to polyandrously. Hypothesis 5 further pre- often necessarily cooperative62,63 interests adult survival, more adult offspring, and dicts in most characterizations of the of females and males? healthier adult offspring for polyandr- hypothesis that the more females mate If no fitness rewards for females of ous than monogamous females, whether the more likely they are to die. multiple paternity exist, the problem of monogamous females mate more than Alternatives to CoR assumptions. It is female multiple mating might indeed be once or not. The basic costs of egg pro- also possible, but not yet experimentally entirely a problem of male-male compet- duction under CoR predict that polyandr- investigated, that male mechanisms affect- itive interactions: which male is the best ous females die faster than monogamous ing females’ reproductive decisions are competitor or which male extracts the females. “nice” rather than “nasty”;49 being things least harm. However, if offspring viability If one assumes that females choose that may enhance, rather than decrease, (i.e., offspring health) matters to prospect- mates for direct benefits (hypothesis 4), female survival. This, according to the ive parents, for example, alternative poten- the CoR predicts no differences in number switch point theorem34 (discussed below), tial mates will often offer females a better of eggs laid, in egg to adult survival, would make females ever “choosier” and or worse shot at healthy offspring.34,62,64 number of adult offspring, and survival less likely to accept encountered potential These alternatives have occasionally been ©of adult offspring2012 for monogamous andLandesmates in the future. And if Bioscience. there are tested,65,66 but seldom in the context of polyandrous females. Hypothesis 4 does independent benefits for females of mul- female lifespan variation,67,68 making it predict, however, a survival benefit for tiple mating that drive their multiple very hard to discern some selectively those females who mate more often, mating in the first place, what might this effective costs. Assuming that there exist whether they are polyandrous or mono- mean to how we theorize the fitness fitness rewards for females of controlling gamous, copulating multiple times with dynamics of female polyandry? Positive their own reproductive decisions, male the same male. Do noteffects on femalesdistribute. may arise because competitive interactions pre- or post- Hypothesis 5: Sexual conflict and competing rivals theoretically may also mating put females in exquisite binds in polyandry. The ad hoc sexual conflict donate with their ejaculates nutritive or which the benefits and costs of polyandry hypotheses often characterize female mul- immune enhancing elements to females.51,52 are in dynamic tension, so that female tiple mating as an interaction between two And these, of course, may enhance female resistance to male control attempts will or several competing males inside the fitness directly.52 Negative effects of evolve49 in evolutionary time or be bodies of females where sperm battle, as ejaculate donations on females are more induced in ecological time.69 though the females are jars. The inside- commonly discussed; but the existence of Hypothesis 6: Compensation theory female mechanisms by which males may negative effects does not mean that posi- says multiple mating enhances offspring decrease the reproductive success of rivals tive effects do not also occur, as they do.27 health with mutual benefits to both sometimes extract costs to females,42 Alternatives might start from the first parents. If the pathogens and parasites sometimes decreasing their survival prob- principle: sex is a necessarily collaborative of the offspring generation are different abilities and making tendencies for female process between two individuals sharing from those of the parental generation, as re-mating to be inhibited.43-48 In this gametes.49,53,54 Or, one might start with expected when pathogens and parasites view, females are caught in the cross-fire the idea that females have power too.49,55 evolve more rapidly than their hosts, the of male rivals, so that the cause of female Could it be that females who multiply “Red Queen’s Challenge” to parents62 is re-mating is only to reduce costs extracted mate in the first place organize and how to produce the best immune systems from pre-mating chasing, so-called “court- manipulate male contests for their own in their offspring. Consideration of basic ship” harassment, or post-mating collateral advantage?56-58 Why not imagine that rules of inheritance of parental alleles cost, not to gain some intrinsic fitness females make the post-copulatory rules of means that in general parents will produce rewards from the mating. The costs to the inside games through their physio- offspring with excellent immune function females of post-copulatory sperm wars are logical organization of the rules and their against the parent generation pathogens.62 through accessory peptides that increase responses to males? Why not cast females What can parents do to increase the female egg-laying and negatively affect not as umpires but players in their multi- likelihood that offspring will have the females’ survival probabilities, which pro- way interactions with males? Indeed, why rare alleles and rare phenotypes that will vides for some scenarios, the only selective not hypothesize that females are “the enhance their survival in the face of novel force of female resistance,49,50 which as architects of sperm competition,”59 a disease risks that arise in the offspring some have noted could indeed have huge reasonable alternative hypothesis, for generation? One route would be mutual

6 Fly Volume 6 Issue 1 mate choice, in which both females and logic suggests that both sexes might multiple mating is common in both sexes. males choose mates complementary (i.e., compensate in cooperative efforts to Assuming large population sizes, demo- dissimilar) to themselves at immune cod- enhance the likelihood of survival of their graphic stochasticity (by chance some ing loci.34,62,63 This option probably works offspring. In species like flies in which individuals die or otherwise leave or enter for large, viscous populations with few post-zygotic parental care is unlikely and populations), and no selection pressures social or ecological constraints on mate unknown, there are nonetheless many against multiple mating, the analytical encounter; however, ecological and social options that individual parents might solution of demographic stochastic mat- impediments to free mate encounter are use facultatively or flexibly to enhance ing theory (DSMT) says that individual ubiquitous, probably vary by species, and offspring survival. From the perspective encounter probability (e) with potential suggest that most parents are making the of CH the remarkable observations of mates, individual survival probability (s), best of a bad job, providing selection favor- Markow and her collaborators of male and the time after mating to receptivity ing variation in parental effects to increase elemental contributions to ovarioles,52 to remating (l ) determine lifetime mating the likelihood that offspring survive long ejaculate-associated nutritive contribu- rates. Under the simplifying assumptions enough to enter the ranks of breeders. tions to females and their offspring51 are of DSMT, differences between individuals The compensation hypothesis (CH)62 particularly interesting. Could the long- and the variance among individuals in (hypothesis 6) says that both female and tails of sperm in the giant sperm species their lifetime mating rates arise from male partners will be under selection sometimes be nutritive as well? Do males differences in the time they have available waged via the success of other parents contribute more when they mate with for mating,64 modulated in all individuals with healthier offspring to compensate females with whom they will produce less of either sex by s, e and l. Thus, multiple for expected offspring viability deficits. In viable offspring? Are these mechanisms mating in either sex can evolve in the D. pseudoobscura, both females and males ones that could be flexibly upregulated in absence of fitness benefits for either sex. discriminate among potential mates,39,40 some matings but not others?54 These From the perspective of DSMT, female ©and when male2012 or female choosers are Landes in questions about the options someBioscience. males multiple mating is no more problematic enforced experimental pairs with a poten- have to collaboratively attempt to than male multiple mating: “it’s all about tial mate they prefer compared with one enhance the reproductive performances time”64 and the ecological and social con- they do not, the pair produce more adult of their mates or even the health of their straints affecting individuals’ time available offspring (but not more eggs) than when mates are intriguing, and as far as I have for mating and reproduction. the chooser is with a potential mate they been able to tell, uninvestigated in terms The DSMT (Hypothesis 7) predicts did not prefer.70 TheseDo observations arenotof their effects distribute. on fitness variation of that there are no differences in egg to inconsistent with the CoR prediction of parents. Perhaps this is not strange given adult survival or in adult offspring survival indiscriminate male D. pseudoobscura, the current hegemony of sexual conflict between monogamous and polyandrous which have the smallest sperm of any and sexual antagonism dominating dis- females (Table 1), and that the number of known Drosophila species. More interest- cussions of the relationships between the adult offspring is greater than or equal ingly, as the CH predicted, females with sexes. Novel insights likely await newer between monogamous and polyandrous males they did not prefer laid more eggs investigations of the nature of these females. Without additional assumptions than females with males they did prefer. potentially collaborative interactions DSMT makes no predictions about life- As a result, even though their offspring between males and females in species like span variation of monogamous and poly- had lower egg-to-adult survival, some of flies that lack post-zygotic parental care. androus females. the offspring survived to breeding age, If multiple mating is a mechanism Hypothesis 8: The switch point the- keeping the lineage of compensating of compensation for offspring viability orem predicts that multiple mating females alive. Laying more eggs to increase deficits, the CH predicts (Table 1) egg to by either sex is adaptive. The DSMT the likelihood that some survive to breed is adult survival and adult offspring survival background certainties of probabilistic a known compensatory mechanism, and is greater in monogamous than polyandr- variation in e, s and l, which produces may levy costs for both sexes of parent ous mating, but that the number of adult real-time changes in the time an individual when environments are challenging.62,63 offspring for monogamous and polyandr- has available for mating34,64,69,71 must also Similar compensatory mechanisms occur ous females is the same, and furthermore shape fitness enhancing mating decisions. in several model vertebrate species as that polyandrous females die sooner than For this to be so, females and males need well as female D. pseudoobscura.63 Like- monogamous females, not just because to discern fitness costs and benefits of wise, CH predicts that polyandrous mat- of enhanced exposure to conspecifics, but mating with this one or that one, given ing provides compensatory benefits to because of the costs of compensation. the unique demographic circumstances of females mating under ecological or social Hypothesis 7: Demographic stochastic each decision-making individual. If indi- contraints.62 mating theory predicts polyandry and viduals discern fitness costs and benefits, Many mechanisms of compensation are polygyny are common in most species. In the switch point theorem (SPT)34 shows possible; some compensatory mechanisms contrast to the intuitive scenarios above, how adaptively flexible individuals evolve are available for both females and males; the axiomatic mating theorem of Hubbell so as to maximize their fitness in contem- others are sex specific. Elementary selection and Johnson71 proved theoretically that porary time; trading off their time available

www.landesbioscience.com Fly 7 for mating with fitness, so that they experiment to control for bench effects. polyandry benefited offspring health, con- sometimes accept and sometimes reject a We controlled for the ages and prior sistent with hypothesis 3 about offspring mating opportunity. The SPT proved experience of males interacting with viability and hypothesis 8, the SPT. This is theoretically that males and females trade MMC and PMC females by rotating the not surprising as both of these off time with fitness gains as they make males in the PMC treatments between ideas depend on an assumption of off- “ ” flexibly adaptive decisions to accept or other PMC females. The study (Gowaty et spring viability as the main component of reject a mating. al., 2010) was simple and tractable, but fitness organizing mating behavior; i.- If individuals make flexible reproduc- large and time consuming, with the oldest e., these two hypotheses are not alter- tive decisions to accept or reject so as to female dying at 138 d old, 131 d after the natives and can be simultaneously so. optimize their fitness given specific demo- start of the experiment. We made the The discussion above stresses the signi- graphic circumstances, as the SPT (Poly- following conclusions: (1) polyandrous ficance of the assumptions of hypotheses. andry hypothesis 8) says, there will be females produced offspring with higher Clearly, in order to explore further the differences in fitness outcomes among probabilities of survival than that of origins and benefits of multiple mating for individuals, but these need not be, in offspring of monogamous females; and females, our collective attention should nature, systematic benefits or costs to (2) polyandrous females did not die be on the various assumptions of these multiple mating relative to single mating significantly faster than monogamous hypotheses. Future strong inference crucial by either sex (Table 2). More important, females. I considered the study important tests33 of these hypotheses will depend the SPT implies that there is no necessary for two reasons. First, it solved the puzzle, upon the veracity of the assumptions of sex differential cost of multiple mating “What do females want”—for D. pseu- each hypothesis. Thus, surely it is the over the cost of single mating for either doobscura, at least. Because we eliminated assumptions of the various hypotheses that sex (Table 2). That there is no further the possibility of multiple-male pre-mating future investigators should attend to. extracted cost in terms of survival of harassment of females, the conclusions ©multiple mating2012 for females is a unique Landeswere unambiguously associated Bioscience. with Next Questions prediction of the switch point theorem females’ mating with multiple, different (Table 1). males compared with one male. Second, it Mechanism and strongly inferential tests showed—to our surprise and for the first of predictive theories of multiple mating Interpreting Results time in any Drosophila species—that in females and males. Gowaty et al. did of Gowaty et al. exposure to and mating with more than not investigate the mechanistic bases for Do notone male wasdistribute. not costly to females. the study results, or whether pre-touching Gowaty et al. demonstrated that mono- Gowaty et al. did not dwell on the mate assessment or preferences predicted gamously mated females with multiple ramifications of the failure of our observa- fitness; we asked no questions about copulations (MMC) had more surviving tions to match the predictions of the CoR mechanisms of sperm competition, offspring than monogamous females and sexual conflict scenarios, nor its physiological post-ejaculatory female res- mated one time (MOC), because single consistency with the predictions of com- istance, variation in ejaculate secondary mated females ran out of sperm before pensation, DSMT or the SPT. The data compounds and their possible negative they died or that sperm were otherwise provided no support for egg-laying predic- or positive effects on females, zygotes and inadequate. Compared with MMC females, tion of hypothesis 1 about sperm limita- offspring were not part of our study. The “ ” PMC females with access to a new male tion or hypothesis 2 about gamete study addressed only the ultimate ques- every day, and who could have mated incompatibilities. Our data are inconsist- tions of fitness variation of alternative with each one and did mate with more ent with hypothesis 4 about direct benefits mating scenarios, not the “proximate” than one male, had offspring with signi- to females of multiple mating, and our mechanisms, except for the proximate ficantly higher egg-to-adult survival and data reject hypothesis 5 of male coercion “ecological” cause of availability to females significantly more offspring that survived of female remating. The data were incon- of males who were potential mates (in to eclosion. Despite our a priori intuition sistent with the hypothesis 6, the CH, but two treatments females had access to only that exposure to more conspecifics would CH advocates might argue that the a single male and in the other multiple ’ decrease PMC females health status and comparison of costs and benefits of males). We necessarily left questions of thus, their lifespan compared with MOC polyandry were an inadequate test of the proximate cause for others, not because and MMC, there were no significant underlying assumptions of the CH, and we are uninterested. Simultaneous study differences in lifespan among the three thus logically not a test of the compensa- of ultimate and proximate causes is an types of experimental females. tion hypothesis. The data over all were ideal, but constraints on funding and All females entered the experimental consistent with hypothesis 7 DSMT, how- time seldom allow, perhaps never have treatments at the same time. All females ever, DSMT could not account for the allowed, simultaneous study of proximate and males were virgin at the start of enhancement of offspring viability via and ultimate questions, particularly in the experiment. We kept trial sets consist- polyandrous mating—at least without demographic context. “ ” ing of paired females who were MOC, an add-on ad hoc assumption. Overall, Sexually symmetric tests of fitness MMC and PMC together throughout the however, the data show explicitly that payouts for multiple mating. Gowaty

8 Fly Volume 6 Issue 1 et al. was necessarily silent about fitness male, would be the same. It would decrease conclusions about the fitness effects of costs and benefits for males, yet a the likelihood that subtle biasing factors different kinds of social exposures. Are symmetric study of female and male associated with inevitable intuitions–about these effects wiped out, one might ask, in subjects would have been much more what males or females ought to do–from the more realistic settings of nature, where powerful in evaluating the intuitive CoR creeping in unnoticed. And, simultaneous hurricanes, predator risk and variation in ideas, which “begin with sex differences to testing of costs and benefits of male multi- food resources and mates might vary? predict further sex differences.” However, ple mating would give our best chance of Probably. But then we are left with only my colleagues and I have a track-record evaluating the effects of social and ecologi- correlational explanations limited to vari- of completed previous sex-symmetric stud- cal constraints on individuals of either sex. ables we are able to measure and have ies using D. pseudoobscura showing the measured in the wild. What we can following: (1) both females and males Next Steps: To Wild Nature hypothesize about such interesting phe- make pre-mating assessments of potential nomena as giant sperm, ejaculate-asso- mates.70 (2) For individual males and Connecting laboratory studies of fitness ciated nutritional donations to females and females, pre-mating assessment (prefer- variation to real-world vagaries of the wild, offspring, ejaculate accessory proteins, or ence) behavior predicts reproductive suc- where social opportunities and ecological explanations for why within species some cess, including offspring health and the constraints mold evolutionary response of females lay more or fewer eggs than others number of offspring that eclose.70 Drosophila sex and evolution, is no easy are enriched with careful laboratory eva- (3) Lifespan variation for males whom task,24 perhaps especially now that we luations of many hypotheses, includ- females preferred or did not prefer and for know that developmental plasticity and ing particularly first principle, axiomatic, females whom males preferred or did not epigenetic responses are so important to quantitative theory that most often yield prefer were statistically indistinguishable, phenotypic evolution.73 Arguing that highly vulnerable crucial predictions. consistent with the conclusion that there laboratory experiments about fitness vari- Starting in the laboratory is probably a ©were not intrinsic2012“quality differences Landes” ation are beside the point misses Bioscience. the truth very good place to begin, but not a good between potential mates who were pre- of what laboratory experiments are good place to end. Our knowledge about flies ferred or not preferred.72 for: namely they give us a precise under- in nature would be enhanced with efforts Gowaty et al. violated our tradition of standing under specifically controlled con- to connect the intriguing results of lab sex-symmetric studies in our study of ditions of how individual reproductive experiments on social behavior—fitness74 female, but not male, multiple mating. success and survival might vary, when and mechanism—to what happens in the So, what would aDo simultaneous testnotmany other distribute. confounding factors are wild. (Table 2) of fitness costs and benefits for removed. In the case of the polyandry female and male subjects possibly tell us? experiment, we removed the confound- Acknowledgments Controlling for notorious “local bench,” ing factors of pre-mating male-male com- I thank Stephen P. Hubbell and Allen diurnal and seasonal effects, simultaneous petitive interactions, as well as overlooked, J. Moore for comments on a previous tests allow a fair comparison between female-female competitive interactions, version of the manuscript. I thank Wyatt the sexes. It would level the playing field and potentially coercive inter-sexual inter- W. Anderson and Yong-Kyu Kim for by asking the same questions of males actions, such as multi-male harassment of years of interesting collaborations on social as we ask of females, in the same way, so that females and mating pairs. In the idealized behavior and fitness of Drosophila. This the experimentally manipulated constraints world, where these sorts of constraints work was partially funded by an NSF grant acting on our subjects, whether female or were removed, we are able to make strong (IOS 0911606).

References 5. Akin E, Levene H, Levine L, Rockwell R. A con- 9. Aspi J, Lankinen P. Frequency of multiple insemina- servative procedure for the estimation of multiple tion in a natural population of Drosophila montana. 1. Anderson WW. Frequent multiple insemination in a insemination in Drosophila. American Naturalist 1984; Hereditas 1992; 117:169-77; PMID:1459857; http:// nutural population of Drosophila pseudoobura.AmNat 124:723-37. dx.doi.org/10.1111/j.1601-5223.1992.tb00171.x 1974; 108:709-11; http://dx.doi.org/10.1086/282949 6. Williams SM, Strobeck C. Measuring the multiple 10. Quezada-Díaz JE, Santos M, Ruiz A, Fontdevila A. 2. Cobbs G. Multiple insemination and male sexual insemination frequency of Drosophila in nature: use The evolutionary history of Drosophia buzzatti.25. selection in natural populations of Drosophila pseuo- of a Y-linked molecular marker. Evolution 1986; 40: Random mating in nature. Heredity 1992; 68:373-9; doobscura. Am Nat 1977; 111:641-56; http://dx.doi. 440-2; http://dx.doi.org/10.2307/2408827 PMID:1563969; http://dx.doi.org/10.1038/hdy.1992. org/10.1086/283197 7. Levine L, Akin E, Olvera O, Gaso MI, Rockwell RF, 53 3. Levine L, Asmussen M, Olvera O, Powell JR, Delarosa Gonzalez F, et al. Chromosomal and behavioral studies 11. Snook RR, Markow TA. Efficiency of gamete usage ME, Salceda VM, et al. of Mexican of Mexican Drosophila. 5. Frequencies of multiple in nature: sperm storage, fertilization and polyspermy. Drosophila 5. A high rate of multiple insemination in insemination in 3 natural populations. Am Nat 1987; Proc Biol Sci 2002; 269:467-73; PMID:11886638; a natural population of Drosophila pseudoobscura.Am 129:458-62; http://dx.doi.org/10.1086/284650 http://dx.doi.org/10.1098/rspb.2001.1854 Nat 1980; 116:493-503; http://dx.doi.org/10.1086/ 8. Kambysellis MP, Craddock EM. Studies of oogenesis 12. Yenisetti SC, Hegde SN. Remating in a Drosophilid: 283644 in natural populations of Drosophilidae. 4. Insemina- Phorticella striata. Kor J Genet 2002; 24:113-8. 4. Loukas M, Vergini Y, Krimbas CB. The genetics of tion patterns in hawaiian Drosophila species (Diptera, 13. Markow TA, Sawka S. Dynamics of mating success drosophila subobscura populations. 18. Multiple Drosophiliadae) correlated with ovarian development. in experimental groups of Drosophila melanogaster insemination and sperm displacements in Drosophila J Insect Behav 1991; 4:83-100; http://dx.doi.org/10. (Diptera, Drosophilidae). J Insect Behav 1992; 5:375- subobscura.. Genetica 1981; 57:29-37; http://dx.doi. 1007/BF01092553 83; http://dx.doi.org/10.1007/BF01049845 org/10.1007/BF00057540

www.landesbioscience.com Fly 9 14. Gromko MH, Markow TA. Courship and remating 33. Platt JR. Strong inference. Science 1964; 146:347-53; 51. Markow TA, Coppola A, Watts TD. How Drosophila in field populations of Drosophila. Anim Behav 1993; PMID:17739513; http://dx.doi.org/10.1126/science. males make eggs: it is elemental. Proc Biol Sci 2001; 45:253-62; http://dx.doi.org/10.1006/anbe.1993.1031 146.3642.347 268:1527-32; PMID:11454298; http://dx.doi.org/10. 15. Markow TA. Evolution of Drosophila mating systems. 34. Gowaty PA, Hubbell SP. Reproductive decisions under 1098/rspb.2001.1673 , Vol 29 1996; 29:73-106. ecological constraints: It’s about time. Proc Natl Acad 52. Markow TA, Ankney PF. Drosophila males contribute 16. Snook RR, Markow TA. Mating system evolution Sci USA 2009; 106:10017-24; PMID:19528648; to oogenesis in a multiple mating species. Science 1984; in sperm-heteromorphic Drosophila. J Insect Physiol http://dx.doi.org/10.1073/pnas.0901130106 224:302-3; PMID:17734916; http://dx.doi.org/10. 2001; 47:957-64; PMID:11472758; http://dx.doi.org/ 35. Dewsbury DA. Ejaculate cost and male choice. Am Nat 1126/science.224.4646.302 10.1016/S0022-1910(01)00070-1 1982; 119:601-10; http://dx.doi.org/10.1086/283938 53. Roughgarden J, Oishi M, Akcay E. Reproductive social 17. Markow TA. Perspective: Female remating, operational 36. Parker GA, Baker RR, Smith VGF. The origin and behavior: cooperative games to replace . sex ratio, and the arena of sexual selection in Droso- evolution of gamete dimorphism and the male-female Science 2006; 311:965-9; PMID:16484485; http://dx. phila species. Evolution 2002; 56:1725-34; PMID: phenomenon. J Theor Biol 1972; 36:529-53; PMID: doi.org/10.1126/science.1110105 12389717 5080448; http://dx.doi.org/10.1016/0022-5193(72) 54. Bono JM, Matzkin LM, Kelleher ES, Markow TA. 18. Rodríguez-Muñoz R. A. Bretman IA, Slate J, Walling 90007-0 Postmating transcriptional changes in reproductive CA, Tregenza T. Natural and sexual selection in a 37. Trivers RL. Parental investment and sexual selection. tracts of con- and heterospecifically mated Drosophila wild insect population. Science 2010; 328:1269-72; In: Campbell B, ed. Sexual selection and the descent of mojavensis females. Proc Natl Acad Sci USA 2011; PMID:20522773; http://dx.doi.org/10.1126/science. man. Chicago: Aldine, 1972:136-79. 108:7878-83; PMID:21518862; http://dx.doi.org/10. 1188102 38. Darwin C. The descent of man and selection in relation 1073/pnas.1100388108 19. House CM, Walling CA, Stamper CE, Moore AJ. to sex. London: John Murray, 1871. 55. Moore AJ, Pizzari T. Quantitative genetic models of Females benefit from multiple mating but not multiple 39. Gowaty PA, Steinichen R, Anderson WW. Mutual sexual conflict based on interacting phenotypes. Am mates in the burying beetle Nicrophorus vespilloides.J interest between the sexes and reproductive success in Nat 2005; 165:S88-97; PMID:15795865; http://dx. Evol Biol 2009; 22:1961-6; PMID:19682308; http:// Drosophila pseudoobscura. Evolution 2002; 56:2537- doi.org/10.1086/429354 dx.doi.org/10.1111/j.1420-9101.2009.01800.x 40; PMID:12583593; http://dx.doi.org/10.1111/j. 56. Hrdy SB. Infanticide among animals: A review, 20. Arnqvist G, Nilsson T. The evolution of polyandry: 0014-3820.2002.tb00178.x classification, and examination of the implications for multiple mating and female fitness in insects. Anim 40. Gowaty PA, Steinichen R, Anderson WW. Indiscri- the reproductive strategies of females. Ethol Sociobiol Behav 2000; 60:145-64; PMID:10973716; http://dx. minate females and choosy males: Within- and 1979; 1:13-40; http://dx.doi.org/10.1016/0162-3095 doi.org/10.1006/anbe.2000.1446 between-species variation in Drosophila. Evolution (79)90004-9 21. Gowaty PA. Beyond extra-pair paternity: individual 2003; 57:2037-45; PMID:14575325 57. Hrdy SB. The woman that never evolved. Cambridge: constraints, fitness components, and social mating 41. Arnold SJ. Bateman principles and the measurement Harvard University Press, 1981. systems. In: Lucas J, Simmons L, eds. Essays on animal of sexual selection in plants and animals. Am Nat 1994; 58. Eberhard EB. Female control: Sexual selection by behavior: Celebrating 50 years of animal behaviour. 144:S126-49; http://dx.doi.org/10.1086/285656 cryptic female choice. Princeton: Princeton University ©Cambridge 2012 University: Cambridge, 2006: 221-56. Landes42. Rice WR. Sexually antagonistic maleBioscience. adaptation Press, 1996. 22. Firman RC, Cheam LY, Simmons LW. Sperm triggered by experimental arrest of female evolution. 59. Gowaty PA. Architects of sperm competition. Trends competition does not influence sperm hook morpho- Nature 1996; 381:232-4; PMID:8622764; http://dx. Ecol Evol 1994; 9:160-2; PMID:21236807; http://dx. logy in selection lines of house mice. J Evol Biol 2011; doi.org/10.1038/381232a0 doi.org/10.1016/0169-5347(94)90076-0 24:856-62; PMID:21306461; http://dx.doi.org/10. 43. Chapman T. Seminal fluid-mediated fitness traits 60. Clark AG, Begun DJ. Female genotypes affect sperm 1111/j.1420-9101.2010.02219.x in Drosophila. Heredity 2001; 87:511-21; PMID: displacement in Drosophila. Genetics 1998; 149:1487- 23. Firman RC, Simmons LW. Sperm competition and the 11869341; http://dx.doi.org/10.1046/j.1365-2540. 93; PMID:9649536 evolution of the sperm hook in house mice. J Evol Biol 2001.00961.x 61. Clark AG, Begun DJ, Prout T. Female x male 2009; 22:2505-11; PMID:19878408;Do http://dx.doi. not44. Chapman T.distribute. The soup in my fly: Evolution, form and interactions in Drosophila sperm competition. Science org/10.1111/j.1420-9101.2009.01867.x function of seminal fluid proteins. PLoS Biol 2008; 1999; 283:217-20; PMID:9880253; http://dx.doi.org/ 24. Markow TA, O’Grady P. Drosophila: A guide to 6:e179-82; PMID:18666830; http://dx.doi.org/10. 10.1126/science.283.5399.217 species identification and use. Academic Press, 2005. 1371/journal.pbio.0060179 62. Gowaty PA. Reproductive compensation. J Evol Biol 25. Bundgaard J, Barker JSF. Remating, sperm transfer, 45. Chapman T, Bangham J, Vinti G, Seifried B, Lung O, 2008; 21:1189-200; PMID:18564347; http://dx.doi. and sperm displacement in the cactophilic species Wolfner MF, et al. The sex peptide of Drosophila org/10.1111/j.1420-9101.2008.01559.x Drosophila buzzatii Patterson & Wheeler (Diptera: melanogaster: Female post-mating responses analyzed 63. Gowaty PA, Anderson WW, Bluhm CK, Drickamer Drosophilidae). Biol J Linn Soc Lond 2000; 71:145- by using RNA interference. Proc Natl Acad Sci USA LC, Kim YK, Moore AJ. The hypothesis of reproduct- 64. 2003; 100:9923-8; PMID:12893873; http://dx.doi. ive compensation and its assumptions about mate 26. Markow TA, O’Grady P. Reproductive ecology of org/10.1073/pnas.1631635100 preferences and offspring viability. Proc Natl Acad Sci Drosophila. Funct Ecol 2008; 22:747-59; http://dx. 46. Chapman T, Davies SJ. Functions and analysis of the USA 2007; 104:15023-7; PMID:17848509; http://dx. doi.org/10.1111/j.1365-2435.2008.01457.x seminal fluid proteins of male Drosophila melano- doi.org/10.1073/pnas.0706622104 27. Lacey Knowles L, Hernandez BB, Markow TA. Non- gaster fruit flies. Peptides 2004; 25:1477-90; PMID: 64. Gowaty PA, Hubbell SP. Chance, time allocation, and antagonistic interactions between the sexes revealed by 15374649; http://dx.doi.org/10.1016/j.peptides.2003. the evolution of adaptively flexible sex role behavior. the ecological consequences of reproductive traits. J 10.023 Integr Comp Biol 2005; 45:931-44; PMID:21676844; Evol Biol 2005; 18:156-61; PMID:15669972; http:// 47. Chapman T, Herndon LA, Heifetz Y, Partridge L, http://dx.doi.org/10.1093/icb/45.5.931 dx.doi.org/10.1111/j.1420-9101.2004.00779.x Wolfner MF. The Acp26Aa seminal fluid protein is 65. Brown WD, Bjork A, Schneider K, Pitnick S. No 28. Markow TA. A comparative investigation of the a modulator of early egg hatchability in Drosophila evidence that polyandry benefits females in Drosophila mating system of Drosophila hydei. Anim Behav 1985; melanogaster. Proc Biol Sci 2001; 268:1647-54; melanogaster.. Evolution 2004; 58:1242-50; PMID: 33:775-81; http://dx.doi.org/10.1016/S0003-3472 PMID:11506676; http://dx.doi.org/10.1098/rspb. 15266973 (85)80010-5 2001.1684 66. Hosken DJ, Stockley P. Benefits of polyandry: A life 29. Bateman AJ. Intra-sexual selection in Drosophila.. 48. Chapman T, Neubaum DM, Wolfner MF, Partridge history perspective. Evol Biol 2003; 33:173-94. Heredity 1948; 2:349-68; PMID:18103134; http:// L. The role of male accessory gland protein Acp36DE 67. Gowaty PA, Kim YK, Rawlings J, Anderson WW. dx.doi.org/10.1038/hdy.1948.21 in sperm competition in Drosophila melanogaster. Proc Polyandry increases offspring viability and mother 30. Tang-Martinez Z, Ryder TB. The problem with Biol Sci 2000; 267:1097-105; PMID:10885514; productivity but does not decrease mother survival in paradigms: Bateman’s worldview as a case study. http://dx.doi.org/10.1098/rspb.2000.1114 Drosophila pseudoobscura. Proc Natl Acad Sci USA Integr Comp Biol 2005; 45:821-30; PMID:21676833; 49. Gowaty PA. Sexual dialectics, sexual selection, and 2010; 107:13771-6; PMID:20643932; http://dx.doi. http://dx.doi.org/10.1093/icb/45.5.821 variation in mating behavior. In: Gowaty PA, ed. org/10.1073/pnas.1006174107 31. Dewsbury DA. The Darwin-Bateman paradigm in Feminism and Evolutionary Biology. New York: 68. Priest NK, Galloway LF, Roach DA. Mating frequency historical context. Integr Comp Biol 2005; 45:831-7; Chapman Hall, 1997:351-84. and inclusive fitness in Drosophila melanogaster. Am PMID:21676834; http://dx.doi.org/10.1093/icb/45.5. 50. Holland B, Rice WR. Perspective: Chase-away sexual Nat 2008; 171:10-21; PMID:18171147; http://dx.doi. 831 selection: antagonistic seduction versus resitance. org/10.1086/523944 32. Snyder BF, Gowaty PA. A reappraisal of Bateman’s Evolution 1998; 52:1-7; http://dx.doi.org/10.2307/ classic study of intrasexual selection. Evolution 2007; 2410914 61:2457-68; PMID:17725639; http://dx.doi.org/10. 1111/j.1558-5646.2007.00212.x

10 Fly Volume 6 Issue 1 69. Gowaty PA, Hubbell SP. Killing time: A mechanism of 71. Hubbell SP, Johnson LK. Environmental variance in 73. West-Eberhard MJ. Developmental plasticity and sexual selection and sexual conflict. In: Leonard J, lifetime mating success, mate choice, and sexual evolution. Oxford: Oxford University Press, 2003. Cordoba-Aguilar A, eds. Primary Sexual Characters in selection. Am Nat 1987; 130:91-112; http://dx.doi. 74. Markow TA. “Cost” of virginity in wild Drosophila Animals Oxford: Oxford University Press, 2010:79-96. org/10.1086/284700 melanogaster females. Ecology and Evolution 2011; 70. Anderson WW, Kim YK, Gowaty PA. Experimental 72. Kim y-K, Weber MB, Anderson WW, Gowaty PA. http://dx.doi.org/10.1002/ece3.54 constraints on mate preferences in Drosophila pseu- No evidence of intrinsic quality differences between doobscura decrease offspring viability and fitness of preferred and non-preferred Drosophila pseudoobscura mated pairs. Proc Natl Acad Sci USA 2007; 104:4484- in tests of mate preferences. Journal of Integrative 8; PMID:17360550; http://dx.doi.org/10.1073/pnas. 2010. In press. 0611152104

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