Research

 

One of our main research themes is sexual selection and the evolution of sexual traits and mating behaviour. In brief, we study male allocation of resources to traits associated with mate acquisition and competitive fertilization, the factors underlying male fitness under competitive conditions, and how male and female reproductive traits have changed over evolutionary time in response to sexual selection. We use comparative, experimental and molecular approaches in a range of organisms.

 

Drosophila prolongata

Sexual selection on condition-dependent traits

Due to immediate fitness benefits, males tend to maximize their investment in ornaments or armaments involved in mate acquisition, and in ejaculate size and quality that can influence competitive fertilization success among rival males. However, these traits tend to be energetically costly, so that males with limited resources available are constrained in their investment, thereby having a fitness disadvantage. Several theoretical models predict that the condition-dependent expression of such costly traits allows females to assess the underlying genetic quality of males and gain genetic benefits for their offspring when mating with the highest-quality males (those with the most exaggerated traits). However, a genetic link between trait expression and male genetic quality has rarely been tested, and nearly nothing is known about the level of condition dependence in postmating sexual traits and how it relates to fitness outcomes. Using quantitative genetic crossing designs in different Drosophila systems, we are addressing the following goals:

  • Quantify genetic variation in male and female quality
  • Quantify condition dependence of sexual and non-sexual traits, including sexual dimorphism
  • Examine intensity of sexual selection on traits relative to their condition dependence
  • Quantify responses to selection using experimental evolution
  • Understand the joint contributions of multiple traits to fitness outcomes

In parallel, using cross-generational experiments, we are testing new theoretical models of sexual selection and condition dependence that are based on non-genetic transmission of male condition effects to the next generation.

Related publications

Audet T, Perdigón Ferreira J, Meena A, Abass M, Torabi-Marashi A, Yeom J, Zaghloul F, Zaghloul N, Mizrahi A, Novikov J, Xi E, Lüpold S & Dworkin I. 2026. Genomic architecture of the developing forelegs of Drosophila prolongata; an exaggerated weapon and ornament. Evolution doi:10.1093/evolut/qpag096

Mukherjee S, De Nardo AN & Lüpold S. 2026. Sex-specific site preferences in response to resource value and conspecific distribution in Drosophila prolongata. Behav Ecol Sociobiol 80: 63.

De Nardo AN, Mukherjee S & Lüpold S. 2026. Condition-dependent success of resource-based reproductive tactics across both sexes in Drosophila prolongata. Behav Ecol Sociobiol 80: 61.

Syed ZA, Gomez RA, Borziak K, Amar A, Cong AS, O'Grady P, Kim BY, Suvorov A, Petrov DA, Lüpold S, Wengert P, McDonough-Goldstein CE, Ahmed-Braimah YH, Dorus S & Pitnick S. 2025. Genomics of a sexually selected male ornament and female preference. Nat Ecol Evol 9: 336-348.

De Nardo AN, Meena A, Maggu K, Eggs B, Sbilordo SH & Lüpold S. 2025. Experimental evolution reveals trade-offs between sexual selection and heat tolerance in Drosophila prolongata. Evolution 79: 823-836.

De Nardo AN, Biswas B, Perdigón Ferreira J, Meena A & Lüpold S. 2025. Socio-ecological context modulates significance of territorial contest competition in Drosophila prolongata. Proc R Soc B 169: 20242501.

Zeender V, Pfammatter S, Roschitzki B, Dorus S & Lüpold S 2023. Genotype-by-environment interactions influence the composition of the Drosophila seminal proteome. Proc R Soc B 290: 20231313.

Zeender V, Sbilordo SH, Roy J & Lüpold S. 2023. Paternal condition affects offspring reproduction and life history in a sex-specific manner in Drosophila melanogaster. Evolution 77: 467-481.

Perdigón Ferreira J, Rohner PT & Lüpold S. 2023. Strongly sexually dimorphic forelegs are not more condition-dependent than less dimorphic traits in Drosophila prolongata. Evol Ecol 37: 493-508.

Perdigón Ferreira J & Lüpold S. 2022. A condition- and context-dependent alternative mating tactic in Drosophila prolongata. Behav Ecol 33: 213-221.

Macartney EL, Zeender V, Meena A, De Nardo AN, Bonduriansky RJ & Lüpold S. 2021. Sperm depletion in relation to developmental nutrition and genotype in Drosophila melanogaster. Evolution 75: 2830-2841.

De Nardo AN, Sbilordo SH, Roy J & Lüpold S. 2021. Condition-dependent interaction between mating success and competitive fertilization success in Drosophila melanogaster. Evolution 75: 2014-2026.

Rohner PT, Teder T, Esperk T, Lüpold S & Blanckenhorn WU. 2018. The evolution of male-biased sexual size dimorphism is associated with increased body size plasticity in males. Funct Ecol 32: 581-591.

Rohner PT, Pitnick S, Snook RR, Blanckenhorn WU, Bächli G & Lüpold S. 2018. Interrelations of global macroecological patterns in wing and thorax size, sexual size dimorphism, and range size of the Drosophilidae. Ecography 41: 1707-1717.

Lüpold S, Manier MK, Puniamoorthy N, Schoff C, Starmer WT, Buckley Luepold SH, Belote JM & Pitnick S. 2016. How sexual selection can drive the evolution of costly sperm ornamentation. Nature 533: 535-538.

Lüpold S, Pitnick S, Berben KS, Blengini CS, Belote JM & Manier MK. 2013. Female mediation of competitive fertilization success in Drosophila melanogaster. Proc Natl Acad Sci USA 110: 10693-10698.

Lüpold S, Manier MK, Berben KS, Smith KJ, Daley BD, Buckley SH, Belote JM & Pitnick S. 2012. How multivariate ejaculate traits determine competitive fertilization success in Drosophila melanogaster. Curr Biol 66: 1607-1617.

Glow-in-the-dark sperm of Drosophila melanogaster

Mechanisms underlying postcopulatory sexual selection and reproductive isolation in Drosophila

We are using Drosophila species as model organisms and apply genetic engineering approaches (i.e., fly populations transformed to produce sperm with green or red fluorescently tagged heads) to study the adaptive significance of intraspecific variation in ejaculate traits. This unique research material enables direct visualization of sperm behavior and fate within their selective environment (i.e., the female reproductive tract) while distinguishing between the sperm from competing males (see VIDEO). So far, our research has demonstrated that (1) males adjust their ejaculates depending on the mating status and reproductive quality of the female; (2) multiple ejaculate traits (e.g., sperm length, velocity and number) are under strong genetic control and, collectively, determine competitive fertilization success, with different ejaculate traits being critical at different stages after female remating; and (3) females can influence the outcome of the competition among ejaculates. More recently, we have also explored the adaptive significance and underlying mechanisms of genetic variation in male × male × female interactions.

In parallel, we have extensively investigated the divergence of the processes underlying conspecific sperm precedence and reproductive isolation among sibling species D. simulans and D. mauritiana. Females of these species show significant differences in the way they store and utilize sperm from different males. Importantly, when males of these different species compete for fertilization in the same female (i.e. conspecific and heterospecific mating), females show a clear preference for sperm of their conspecific mate through differential sperm storage and use. Diversifying (allopatric) postcopulatory sexual selection thus seems to quickly result in reproductive isolation. Combined with the detailed intraspecific examination, our results greatly advance our knowledge of the fundamental microevolutionary processes underlying the important macroevolutionary patterns of biodiversity, which are receiving growing attention in studies of sexual selection.

Related publications

Daupagne L, Winkler L, Pembury-Smith MQ, Lüpold S, Snook RR & Fitzpatrick JL. 2025. One size does not fit all: female–male interactions on the path to fertilization. Reproduction 169: e240238.

Mahdjoub H, Khelifa R, Roy J, Sbilordo SH, Zeender V, Perdigón Ferreira J, Gourgoulianni N & Lüpold S 2023. Interplay between male quality and male-female compatibility in female choice across episodes of selection. Sci Adv 9: eadf5559.

Lüpold S, Reil JB, Manier MK, Zeender V, Belote JM & Pitnick S. 2020. How female × male and male × male interactions influence competitive fertilization in Drosophila melanogaster. Evol Lett 4: 416-429.

Lüpold S, Manier MK, Puniamoorthy N, Schoff C, Starmer WT, Buckley Luepold SH, Belote JM & Pitnick S. 2016. How sexual selection can drive the evolution of costly sperm ornamentation. Nature 533: 535-538.

Manier MK, Lüpold S, Belote JM, Starmer WT, Berben KS, Ala-Honkola O, Collins WF & Pitnick S. 2013. Postcopulatory sexual selection generates speciation phenotypes in Drosophila. Curr Biol 23: 1853-1862.

Lüpold S, Pitnick S, Berben KS, Blengini CS, Belote JM & Manier MK. 2013. Female mediation of competitive fertilization success in Drosophila melanogaster. Proc Natl Acad Sci USA 110: 10693-10698.

Manier MK, Lüpold S, Pitnick S & Starmer WT. 2013. An analytical framework for estimating fertilization bias and the fertilization set from multiple sperm-storage organs. Am Nat 182:552-561.

Manier MK, Belote JM, Lüpold S, Ala-Honkola O, Berben KS, Collins WF & Pitnick S. 2013. Rapid diversification of sperm precedence traits and processes among three sibling Drosophila species. Evolution 67: 2348-2362.

Lüpold S, Manier MK, Berben KS, Smith KJ, Daley BD, Buckley SH, Belote JM & Pitnick S. 2012. How multivariate ejaculate traits determine competitive fertilization success in Drosophila melanogaster. Curr Biol 66: 1607-1617.

Droge-Young EM, Manier MK, Lüpold S, Belote JM & Pitnick S. 2012. Covariance among premating, post-copulatory and viability fitness components in Drosophila melanogaster and their influence on paternity measurement. J Evol Biol 25: 1555-1563.

Lüpold S, Manier MK, Ala-Honkola O, Belote JM & Pitnick S. 2011. Male Drosophila melanogaster adjust ejaculate size based on female mating status, fecundity, and age. Behav Ecol 22: 184-191.

Fly vials in incubator

Thermal fertility

Insects and other ectothermic species, whose physiology and metabolism are governed by ambient temperatures, are particularly vulnerable to the increasingly frequent and intense heat events. As fertility is more sensitive to thermal stress than survival, we are studying the thermal fertilit limits and processes underlying thermal fertility loss in both males and females exposed to sublethal temperature stress, using experimental work on insect model systems. In parallel, we are actively collaborating on various meta-analyses on the topic within the European Thermal Fertility Network, an ESEB-sponsored Special Topics Network, to gain a broader and more general understanding of these patterns.

Related publications

Meena A, Maggu K, De Nardo AN, Kovalov V, Eggs B & Lüpold S. 2025. Stage-specific and cumulative effects of heat stress on male and female reproductive performance in Drosophila melanogaster. J Thermal Biol 132: 104001.

De Nardo AN, Meena A, Maggu K, Eggs B, Sbilordo SH & Lüpold S. 2025. Experimental evolution reveals trade-offs between sexual selection and heat tolerance in Drosophila prolongata. Evolution 79: 823-836.

Meena A, Maggu K, De Nardo AN, Sbilordo SH, Eggs B, Al Toma Sho R & Lüpold S. 2024. Life stage-specific effects of heat stress on spermatogenesis and oogenesis in Drosophila melanogaster. J Thermal Biol 125: 104001.

Meena A, De Nardo AN, Maggu K, Sbilordo SH, Snook RR & Lüpold S. 2024. Fertility loss and recovery dynamics after repeated heat stress across life stages in male Drosophila melanogaster: Patterns and processes. R Soc Open Sci 11: 241082.

Dougherty LR, ... Lüpold S et al. (44 authors). 2024. A systematic map of studies testing the relationship between temperature and animal reproduction. Ecol Solut Evid 5: e12303.

Microbial effects on host reproduction

Phenotypes are shaped by their underlying genes, their environment and, as is becoming increasingly clear, by the microbes living in and on them (i.e., microbiota). Particularly the gut microbiota has emerged as an influential contributor to nearly any aspect of its host's life. Sexually transmitted pathogens also play a pivotal role and are extensively studied in both medicine and evolutionary ecology. Surprisingly little is known, however, about the influence of commensal microbes on their host's reproductive health, and, if sexually transmitted, how they interact with the microbiota of their host's sexual partners. Such interactions could have profound fitness consequences for both mates, either directly or mediated by any modulation of the reproductive function. Changes in the reproductive performance could be particularly consequential for males in species in which females mate multiply and thus cause sperm from different males to compete for fertilization. We are studying how the diversity and composition of commensal bacteria influence male reproductive investments and fitness, using wild-caught and lab-reared Drosophila as a study system. We further explore the extent of sexual transmission of bacteria and manipulate the microbial composition to study the effect of representative strains on various male reproductive traits, from sperm quality or composition of the seminal fluid to competitive fertilization success.

Related publications

Maggu K, Meena A, De Nardo AN, Sbilordo SH, Al Toma Sho R & Lüpold S. 2025. Microbiome-mediated resilience and cross-generational consequences in male Drosophila exposed to combined environmental stressors. bioRxiv doi:10.1101/2025.05.16.654542.

Maggu K, Meena A, De Nardo AN, Sbilordo SH, Roy J & Lüpold S. 2025. Male gut microbiome mediates postmating sexual selection in Drosophila. bioRxiv doi:10.1101/2025.05.23.655737.

Within-male sperm selection: The role of genetic variation among 'sibling' sperm

That sperm quality varies widely between individuals is no surprise. But what about different sperm of a given male? Only a small fraction of all sperm transferred will ever reach the ovum. Is this a random selection or are some sperm simply more likely to get there? Since each sperm only carries the haploid genome, it will pass either the maternal or paternal allele on to the next generation. Any genetic differences that could affect sperm quality and thus the likelihood of fertilization could promote selection for these variants. However, to date, clear-cut experimental evidence is limited. We are developing a system in Drosophila fruit flies that will allow us to unambiguously detect haploid selection if it exists. Genes that are expressed post-meiotically (i.e. at the haploid stage) are the most likely targets of haploid selection as these they are less likely to synchronize gene products through exchange via cytoplasmic bridges. Therefore, we use genetic manipulation to fluorescently label different alleles of the same gene. If expressed post-meiotically, fluorescent colours should be mixed, otherwise both colours would be found in each sperm cell. We combine this approach with quantitative PCR techniques of wild-type flies to test how sperm are used by females after mating with a heterozygous male.

Related publications

Since the project started only recently, there are no publications yet.

Mule deer. Photo credit: Rich Keen / DPRA

Trade-offs among reproductive investments

Whatever resources an individual invests in one trait, it cannot invest in others. Consequently, trade-offs in resource allocation are often predicted. However, comparisons between individuals or species can become more complicated, because some may simply have more resources available to invest overall than others, which can result in positive rather than negative relationships between traits. Similarly, some traits can be positively related and, jointly, trade off against other, possibly unmeasured traits. We are interested in understanding how different, energetically costly traits are associated with one another and how selection shapes these relationships. We are focusing primarily on combinations of reproductive traits, for example sperm number vs. sperm size or premating vs. postmating sexual traits (e.g., male weapons vs. testes), given that males attempt to maximize their investment in all these traits due to their direct fitness benefits.

In recent work using meta-analytical tools, we have shown that the trade-off between sperm size and number depends on the mechanism of postmating sexual selection and the space at the site of fertilization relative to the numbers of sperm competing. Selection in large organisms tends to disproportionately favour sperm number over sperm length, because sperm risk being lost or diluted in the spacious female reproductive tract. Small organisms, with limited space, tend to show a reversed pattern. Transferring more competitive sperm, able to displace rival sperm from storage, appears to be a better strategy than simply increasing sperm quantity and having excess sperm never even reaching storage. Similarly, we have shown how the male's ability to monopolize females changes relative allocation to pre- and postmating sexual traits. Relative to premating weapons, testes become increasingly important as the ability of warding off rival males declines and the risk of sperm competition increases. So, the relationship between pre- and postmating sexual traits can vary between strongly positive and strongly negative.

Related publications

Grueter CC, Qi X & Lüpold S. 2026. Effects of between-group competition on sexual size dimorphism in primates. Biol Lett 22: 20250680.

Grueter CC & Lüpold S. 2024. The role of between-group signalling in the evolution of primate ornamentation. Evol Lett 8: 927-935.

Valencia-Aguilar A, Ringler E, Lüpold S, Guayasamin JM & Prado CP. 2024. Evolutionary trade-offs between testes size and parenting in Neotropical glassfrogs. Proc R Soc B 291: 20240054.

Aguiar PL, Lüpold S & Nali RC. 2023. Relationships between vocalization characteristics and sperm traits in a neotropical treefrog. Evol Ecol 37: 797-813.

Liao WB, Jiang Y, Jin L & Lüpold S. 2023. How hibernation in frogs drives brain and reproductive evolution in opposite directions. eLife 12: RP88236.

Reuland C, Simmons LW, Lüpold S* & Fitzpatrick JL*. 2021. Weapons evolve faster than sperm in bovids and cervids. Cells 10: 1062. (*shared last-authorship)

Liao WB, Zhong MJ & Lüpold S. 2019. Sperm quality and quantity evolve through different selective processes in the Phasianidae. Sci Rep 9: 19278.

Lüpold S, Simmons LW & Grueter CC. 2019. Sexual ornaments but not weapons trade off against testes size in primates. Proc R Soc B 286: 20182542.

Simmons LW, Lüpold S & Fitzpatrick JL. 2017. Evolutionary trade-off between secondary sexual traits and ejaculates. Trends Ecol Evol 32: 964-976.

Lüpold S, Jin L & Liao WB. 2017. Population density and structure drive differential investment in pre- and postmating sexual traits in frogs. Evolution 71: 1686-1699.

Lüpold S & Fitzpatrick JL. 2015. Sperm size trumps sperm number in mammalian ejaculate evolution. Proc R Soc B 282: 20152122.

Lüpold S, Simmons LW, Tomkins JL & Fitzpatrick JL. 2015. No evidence for a trade-off between sperm length and male premating weaponry. J Evol Biol 28: 2187-2195.

Fitzpatrick JL & Lüpold S. 2014. Sexual selection and the evolution of ejaculate quality. Mol Human Reprod 20: 1180-1189.

Lüpold S, Tomkins JL, Simmons LW & Fitzpatrick JL. 2014. Female monopolization mediates the relationship between pre- and postcopulatory sexual traits. Nat Commun 5: 3184.

Lüpold S. 2013. Ejaculate quality and constraints in relation to sperm competition levels among eutherian mammals. Evolution 67: 3052-3060.

Immler S, Pitnick S, Parker GA, Durrant KL, Lüpold S, Calhim S & Birkhead TR. 2011. Resolving variation in the reproductive tradeoff between sperm size and number. Proc Natl Acad Sci USA 108: 5325-5330.

Evolution of reproductive traits in birds

Our earlier research also focused on understanding the processes underlying the stunning diversification in sperm morphology and its associations with sperm function in passerine birds. For example, in comparative studies, focusing primarily of New World Blackbirds (Icteridae), we have shown how sperm morphology is shaped through postcopulatory sexual selection, possibly because longer sperm can swim faster (and thus potentially have a fertilization advantage). Associated with this variation in sperm morphology and selection for longer and greater numbers of sperm through sperm competition, we also found adaptations in testicular morphology and spermatogenic efficiency. Importantly, various constraints in sperm production can result in trade-offs between sperm size and number, but the way these trade-offs manifest themselves depends on the conditions at the site of fertilization and the processes of sperm competition.

We have also documented systematic variation in sperm morphology across the species range of the red-winged blackbird (Agelaius phoeniceus). This species exhibits among-population diversity in mating systems, and our results suggest that the sperm diversity may track the expansion of this species from its origin. Finally, although sperm size and shape are typically assumed to be consistent within males, we have shown in the same species that sperm morphology, velocity and quantity can be phenotypically and adaptively plastic across the breeding season.

Related publications

Lüpold S, de Boer RA, Evans JP, Tomkins JL & Fitzpatrick JL. 2020. How sperm competition shapes the evolution of testes and sperm: A meta-analysis. Phil Trans R Soc B 375: 20200064.

Liao WB, Zhong MJ & Lüpold S. 2019. Sperm quality and quantity evolve through different selective processes in the Phasianidae. Sci Rep 9: 19278.

Lüpold S & Pitnick S. 2018. Sperm form and function: what do we know about the role of sexual selection? Reproduction 155: R229-R243. (Invited review)

Fitzpatrick JL & Lüpold S. 2014. Sexual selection and the evolution of ejaculate quality. Mol Human Reprod 20: 1180-1189.

Lüpold S, Birkhead TR, Westneat DF. 2012. Seasonal variation in ejaculate traits of male red-winged blackbirds (Agelaius phoeniceus). Behav Ecol Sociobiol 66: 1607-1617.

Immler S, Pitnick S, Parker GA, Durrant KL, Lüpold S, Calhim S & Birkhead TR. 2011. Resolving variation in the reproductive tradeoff between sperm size and number. Proc Natl Acad Sci USA 108: 5325-5330.

Lüpold S, Wistuba J, Damm OS, Rivers JW & Birkhead TR. 2011. Sperm competition leads to functional adaptations in avian testes to maximize sperm quantity and quality. Reproduction 141: 595-605.

Lüpold S, Westneat DF & Birkhead TR. 2011. Geographical variation in sperm morphology in the redwinged blackbird (Agelaius phoeniceus). Evol Ecol 25: 373-390.

Lüpold S, Calhim S, Immler S & Birkhead, TR. 2009. Sperm morphology and sperm velocity in passerine birds. Proc R Soc Lond B 276: 1175-1181.

Lüpold S, Linz GM & Birkhead TR. 2009. Sperm design and variation in the New World blackbirds (Icteridae). Behav Ecol Sociobiol 63: 899-909.

Lüpold S, Linz GM, Rivers JW, Westneat DF & Birkhead TR. 2009. Sperm competition selects beyond relative testes size in birds. Evolution 63: 391-402.