My research focuses on the origins and maintenance of biodiversity, using butterflies and their host plants as a study system. I am particularly interested in how geography, ecology and genetics interact to drive the evolution of new forms and species.
Although gene flow tends to homogenize populations, it may also contribute to adaptation and even drive speciation if introgressed variants cause reproductive isolation. We tested this hypothesis by combining introgression analysis with QTL mapping to uncover the genomic regions encoding adaptive traits in Heliconius butterflies, including color pattern, host plant preference, sex pheromones, wing shape, flight dynamics and mate choice.
We found that H. elevatus is a hybrid species that has persisted for ~180 kya. This is despite pervasive and on-going gene flow with one parent, H. pardalinus, which homogenizes 99% of their genomes. The integrity of H. elevatus is maintained by the remaining 1%, which introgressed from H. melpomene, and is spread widely across the genome in islands of divergence. These islands harbor species-specific traits, and adaptive coupling among them spreads the effects of selection across the genome, allowing multiple genomic regions to evolve as a coadapted unit and overcome gene flow.
Rosser et al. (2015) Extensive range overlap between Heliconius sister species: evidence for sympatric speciation in butterflies? BMC Evolutionary Biology 15:125.
Rosser et al. (2019) Geographic contrasts between pre- and postzygotic barriers are consistent with reinforcement in Heliconius butterflies. Evolution 73(9):1821-1838.
Rosser et al. Hybrid speciation driven by multilocus introgression. Nature In press
Figure | a) A multispecies coalescent model finds H. elevatus to be a hybrid species, and it is sympatric with both its parents. b) Example of an introgressed cluster of species-specific traits: wing shape, sex pheromones and male preference all map to a QTL on chromosome 20; phylogenetic topologies (top) show this locus derives from H. melpomene
Understanding speciation requires identifying the reproductive barriers between taxa and elucidating their genetics. However, which kinds of barriers evolve may depend on the extent of geographic isolation. We performed the first genome-wide analysis of the genetics of hybrid sterility in Lepidoptera and showed that female sterility between allopatric populations of H. pardalinus is produced by complex epistatic interactions involving the sex chromosome. Counterintuitively, recombined sex chromosomes rescue hybrid fitness.
We recently replicated this result using unrelated swallowtail butterflies (the cover image to the right shows the developing ovary of Papilio polytes). We present a mathematical model showing how a polygenic sex-linked architecture coupled with imbalanced introgression between the sex chromosome and autosomes can explain our results, as well as the “Two rules of speciation”: Haldane’s Rule and the large X effect.
Rosser et al. (2019) Geographic contrasts between pre- and postzygotic barriers are consistent with reinforcement in Heliconius butterflies. Evolution 73(9):1821-1838.
Rosser N et al. (2022) Complex basis of hybrid female sterility and Haldane’s rule in Heliconius: butterflies: Z-linkage and epistasis. Molecular Ecology 31(3):959-977.
Xiong T et al. (2022) A polygenic explanation for Haldane’s rule in butterflies (2023). PNAS 120(44).
Figure | a) An interaction between loci at either ends of the sex chromosome predicts hybrid fertility b) Recombined haplotypes (ZBS and ZSB) have higher fitness than unrecombined haplotypes (ZBB and ZSS)
The Amazon basin contains few obvious geographic barriers, yet it is the most biodiverse region on Earth. In heliconiine butterflies, maps made from museum specimens show that hybrid zones are often clustered around large rivers, implying that they may drive or maintain population differentiation. However, maps of sampling effort also show a strong bias towards rivers, thus the pattern could also be an artifact.
Together with Prof. A. Freitas’ lab at the University of Campinas, I collected field samples along a 900km transect and showed that the Amazon river is indeed a biogeographic “suture zone” (an area where hybrid and contact zones of multiple taxa are clustered). This supports the riverine barrier hypothesis for high diversity in the Amazon, which dates back to Alfred Russell Wallace. We publicised the findings through an outreach film (below), which highlighted the critical importance of museums as invaluable resources of information on biodiversity.
Rosser N et al. (2012) Testing historical explanations for gradients in species richness in heliconiine butterflies of tropical America. Biological Journal of the Linnean Society 105:479-497.
Rosser N et al. (2014) Stable Heliconius butterfly hybrid zones are correlated with a local rainfall peak at the edge of the Amazon basin. Evolution 68(12):3470-3484.
Rosser N et al. (2021) The Amazon river is a suture zone for a polyphyletic group of co-mimetic heliconiine butterflies. Ecography 44(2):177-187.
Rosser N, Seixas F + 23 authors + Mallet, J & Dasmahapatra KK. Hybrid speciation driven by multilocus introgression of ecological traits (2024). Nature In press.
Page E, Queste L, Rosser N, Mallet J, Srygley RB, McMillan OW & Dasmahapatra KK. Pervasive mimicry in flight behaviour among aposematic butterflies (2024). PNAS 121(11).
Xiong T, Tarikere S, Rosser N, Li X, Yago M & Mallet J. A polygenic explanation for Haldane’s rule in butterflies (2023). PNAS 120(44).
Costa M, Viloria AL, Neild AFE, Rosser N, Attal S, Benmesbah M & Lamas G. Lepidoptera from the Pantepui. Part XIV. A new subspecies of Heliconius elevatus Nöldner, 1901 (2023). Antenor 10 (2): 56-72.
Sierra-Botero L, Calonje M, Robbins RK, Rosser N, Pierce NE, López-Gallego C & Valencia-Montoya WA. (2023). Cycad phylogeny predicts host plant use of Eumaeus butterflie. Ecology and Evolution 13:e9978.
Xiong T, Tarikere S, Rosser N, Li X, Yago M & Mallet J (2022). Diverse genetic architectures on the Z chromosome underlie the two rules of speciation in swallowtail butterfly hybrids. bioRxiv doi: https://doi.org/10.1101/2022.10.28.514284.
Naka LN, Werneck F, Rosser N, Pil MW & Boubli JP (2022). The Role of Rivers in the Origins, Evolution, Adaptation, and Distribution of Biodiversity. Frontiers in Ecology and Evolution 10:1035859.
Rosser N, Seixas F & Mallet J (2022). Sympatric speciation by allochrony? Molecular Ecology 31:3975–3978.
Rosser N, Edelman N, Queste LM, Nelson M, Seixas F, Dasmahapatra KK & Mallet J (2022). Complex basis of hybrid female sterility and Haldane’s rule in Heliconius: butterflies: Z-linkage and epistasis. Molecular Ecology 31(3):959-977.
Rosser N, Shirai LT, Dasmahapatra KK, Mallet J & Freitas AV (2021). The Amazon river is a suture zone for a polyphyletic group of co-mimetic heliconiine butterflies. Ecography 44(2):177-187.
Rosser N, Queste LM, Cama B, Edelman NB, Mann F, Mori Pezo R, Morris J, Segami C, Velado P, Schulz S, Mallet J & Dasmahapatra KK (2019). Geographic contrasts between pre- and postzygotic barriers are consistent with reinforcement in Heliconius butterflies. Evolution 73(9):1821-1838.
Freitas AVL, Ramos RR, Silva-Brandão KL, Coutoné MN, Magaldi LM, Rosser N & Brown KS (2019). A new subspecies of Heliconius hermathena (Nymphalidae: Heliconiinae) from Southern Amazonia. Neotropical Entomology 48(3):467-475.
Rosser N, Freitas AVL, Huertas B, Joron M, Lamas G, Mérot C, Simpson F, Willmott KR, Mallet J and Dasmahapatra KK (2019). Cryptic speciation associated with geographic and ecological divergence in two Amazonian Heliconius butterflies. Zoological Journal of the Linnean Society 186(1):233-249.
Bernal, XE et al. Empowering Latina scientists (2019). Science 363:825-826.
Rosser N & Mori Pezo R (2017). Colour pattern divergence in Napeocles jucunda Hübner, 1808 is associated with shifts in behaviour, host plant and habitat. Tropical Lepidoptera Research 27(2):106-110.
Schulz S, Vanjari S, Rosser N, Mann S, Dasmahapatra K, Linares M, Pardo-Diaz C, Salazar C, Jiggins C & Mann F (2017). The scent chemistry of Heliconius wing androconia. Journal of Chemical Ecology 43(9):843-857.
Rosser N (2017). Shortcuts in biodiversity research: What determines the performance of higher taxa as surrogates for species? Ecology and Evolution 7(8):2595-2603.
Arias M, Meichanetzoglou A, Elias M, Rosser N, de-Silva DL, Nay B & Llaurens V (2016) Variation in cyanogenic compounds concentration within a Heliconius butterfly community: does mimicry explain everything? BMC Evolutionary Biology 16:272.
Arias M, le Poul Y, Chouteau M, Boisseau R, Rosser N, Théry M, & Llaurens V. (2016). Crossing fitness valleys: empirical estimation of a fitness landscape associated with polymorphic mimicry. Proceedings of the Royal Society B 283:20160391.
Merrill R et al. (2015). The diversification of Heliconius butterflies: What have we learned in 150 years? Journal of Evolutionary Biology 28(8):1417-38.
Rosser N, Kozak KM, Phillimore AB & Mallet J (2015). Extensive range overlap between Heliconius sister species: evidence for sympatric speciation in butterflies? BMC Evolutionary Biology 15:125.
Rosser N, Dasmahapatra K & Mallet, J (2014). Stable Heliconius butterfly hybrid zones are correlated with a local rainfall peak at the edge of the Amazon basin. Evolution 68(12):3470-84.
Green JP, Leadbeater L, Carruthers JP, Rosser N, Lucas ER & Field J (2013). Clypeal patterning in the paper wasp Polistes dominulus: no evidence of adaptive value in the wild. Behavioural Ecology 24(3):623-633.
Heliconius Genome Consortium (2012). A butterfly genome reveals promiscuous exchange of mimicry adaptations among species. Nature 487:94-98.
Rosser N, Phillimore AB, Huertas B, Willmott KR, & Mallet J (2012). Testing historical explanations for gradients in species richness in heliconiine butterflies of tropical America. Biological Journal of the Linnean Society 105:479-497.
Rosser N & Eggleton P (2012). Can higher taxa be used as a surrogate for species-level data in biodiversity surveys of litter/soil insects? Journal of Insect Conservation 16:87-92.
Leadbeater E, Carruthers JM, Green JP, Rosser N & Field J (2011). Nest inheritance is the missing source of direct fitness in a primitively eusocial insect. Science 333:874-876.
University College London
Ph.D. in Genetics
Imperial College & the Natural History Museum, London
M.Sc. in Taxonomy and Biodiversity
University of East Anglia
B.Sc. in Ecology