Many tropical environments experience cyclical seasonal changes, frequently with pronounced wet and dry seasons, leading to a highly uneven temporal distribution of resources. Short‐lived animals inhabiting such environments often show season‐specific adaptations to cope with alternating selection pressures. African Bicyclus butterflies show strong seasonal polyphenism in a suite of phenotypic and life‐history traits, and their adults are thought to undergo reproductive diapause associated with the lack of available larval host plants during the dry season. Using 3 years of longitudinal field data for three species in Malawi, dissections demonstrated that one forest species reproduces continuously, whereas two savannah species undergo reproductive diapause in the dry season, either with or without pre‐diapause mating. Using additional data from field‐collected and museum samples, we then documented the same three mating strategies for a further 37 species. Phylogenetic analyses indicated that the ancestral state was a non‐diapausing forest species, and that habitat preference and mating strategy evolved in a correlated fashion. Bicyclus butterflies underwent rapid diversification during the Late Miocene, coinciding with expansions into more open savannah habitat. We conclude that the ability to undergo reproductive diapause was a key trait that facilitated colonization and eventual radiation into savannahs in the Late Miocene.

Phenotypic plasticity in heterogeneous environments can provide tight environment‐phenotype matching. However, the prerequisite is a reliable environmental cue(s) that enables organisms to use current environmental information to induce the development of a phenotype with high fitness in a forthcoming environment. Here, we quantify predictability in the timing of precipitation and temperature change to examine how this is associated with seasonal polyphenism in tropical Mycalesina butterflies. Seasonal precipitation in the tropics typically results in distinct selective environments, the wet and dry seasons, and changes in temperature can be a major environmental cue. We sampled communities of Mycalesina butterflies from two seasonal locations and one aseasonal location. Quantifying environmental predictability using wavelet analysis and Colwell's indices confirmed a strong periodicity of precipitation over a 12‐month period at both seasonal locations compared to the aseasonal one. However, temperature seasonality and periodicity differed between the two seasonal locations. We further show that: (a) most females from both seasonal locations synchronize their reproduction with the seasons by breeding in the wet season but arresting reproduction in the dry season. In contrast, all species breed throughout the year in the aseasonal location and (b) species from the seasonal locations, but not those from the aseasonal location, exhibited polyphenism in wing pattern traits (eyespot size). We conclude that seasonal precipitation and its predictability are primary factors shaping the evolution of polyphenism in Mycalesina butterflies, and populations or species secondarily evolve local adaptations for cue use that depend on the local variation in the environment.

New ecological niches that may arise due to climate change can trigger diversification, but their colonisation often requires adaptations in a suite of life-history traits. We test this hypothesis in species-rich Mycalesina butterflies that have undergone parallel radiations in Africa, Asia, and Madagascar. First, our ancestral state reconstruction of habitat preference, using c. 85% of extant species, revealed that early forest-linked lineages began to invade seasonal savannahs during the late Miocene-Pliocene. Second, rearing replicate pairs of forest and savannah species from the African and Malagasy radiation in a common garden experiment, and utilising published data from the Asian radiation, demonstrated that savannah species consistently develop faster, have smaller bodies, higher fecundity with an earlier investment in reproduction, and reduced longevity, compared to forest species across all three radiations. We argue that time-constraints for reproduction favoured the evolution of a faster pace-of-life in savannah species that facilitated their persistence in seasonal habitats.

http://www.eje.cz host-plant specialization will be an important determinant of traits involved in insect-plant interactions (Gripenberg et al., 2010, Schäpers et al., 2016.Oviposition preferences tend to be under strong selection in the wild because performance of larvae (Singer, 2004) and resulting adults (Scheirs et al., 2000) tends to vary greatly on the different species of plants on which the larvae develop. Indeed, experimental studies indicate a general congruence between oviposition preferences and larval performance (Thompson, 1988;Friberg & Wiklund, 2009;Gripenberg et al., 2010). However, oviposition preferences are not always strongly correlated with particular measures of larval performance, especially in host-plant generalists (Gripenberg et al., 2010). This is perhaps in part because host-plant generalists are under selection to make oviposition decisions that are adaptive over a wide range of host-plant species, and thus may use oviposition cues that are not optimal for each particular potential host. While more specialized dicotyledonous plant feeders often use particular chemicals that are characteristic of particu-

Author contributions: SH, PMB and OB designed the study; SH carried out the experiment;EvB and OB collected data for habitat preference; CJB wrote a custom ImageJ macro; OB made figure illustrations; SH and EvB carried out analyses and wrote the manuscript with inputs from CJB, PMB and OB. All authors read and approved the final version of the manuscript. 2 ABSTRACTGlobal change can trigger shifts in habitat stability and shape the evolution of organismal lifehistory strategies, with unstable habitats typically favouring a faster pace-of-life. We test this hypothesis in species-rich Mycalesina butterflies that have undergone parallel radiations in Africa, Asia, and Madagascar. First, our ancestral state reconstruction of habitat preference, using ~85% of extant species, revealed that early forest-linked lineages began to invade seasonal savannahs during the Late Miocene-Pliocene. Second, rearing replicate pairs of forest and savannah species from the African and Malagasy radiation in a common garden experiment, and utilising published data from the Asian radiation, demonstrated that savannah species consistently develop faster, have smaller bodies, higher fecundity with an earlier investment in reproduction, and reduced longevity, compared to forest species across all three radiations. We argue that time-constraints for reproduction favoured the evolution of a faster pace-of-life in savannah species that facilitated their persistence in seasonal habitats.