THE EVOLUTION OF MORPHOLOGICAL DIVERSITY AND SEXUAL DIMORPHISM IN STICK AND LEAF INSECTS

How has the diversity of life forms come to be? This question is at the core of evolutionary biology and can be addressed at different scales: by studying the processes that drive modifications within populations of organisms generation after generation (microevolution), or by investigating patterns of changes on the tree of life over long periods of time (macroevolution). Understanding the ultimate drivers of morphological diversity eventually entails connecting microevolutionary processes with macroevolutionary patterns. My dissertation investigates the diversification of body and egg form and its drivers in a relatively small but particularly diverse insect order: the stick and leaf insects (Phasmatodea). As masters of camouflage, the 3,400 described species of phasmids are an ideal system to study morphological evolution as they vary tremendously in body morphology, going from long slender branch mimics to wide, flat animals that look exactly like leaves. This remarkable diversity of forms enables phasmids to avoid detection by visually-hunting predators. Even their remarkably diverse hardshelled eggs resemble a wide variety of plant seeds. In addition, males and females of the same species often look very different from each other, with females in extreme cases more than ten times the size of the males. In chapters one, two and three, I investigate the patterns of variation of female body morphology, sexual dimorphism and egg morphology respectively, and potential ecological, life history and biomechanical correlates in a phylogenetic context. I describe repeated convergence towards multiple body forms associated with habitat transitions but find substantial variation in the strength of convergence and underlying evolutionary paths. Then, I show that variation in the extent of sexual dimorphism is best explained by variation in selective pressures acting on males, namely locomotor (flight) performance and male competition (sexual selection). Finally, I show that variation in egg size and shape is driven by variation in life history strategies, mechanical constraints and oviposition strategy. In chapters four, five and six, I investigate the microevolutionary processes behind the primary macroevolutionary forces driving variation in sexual dimorphism. In chapter four, I show in leaf insects (Phyllium philippinicum) that larger males are poor flyers, suggesting that selection for flight performance favors smaller male body sizes in this species, and reinforcing the broader taxonomic findings of chapter two. In chapters five and six, I describe how a change in the mating system of thorny devil stick insects (Eurycantha calcarata) switched the direction of sexual selection and led to the evolution of exceptionally large male body sizes and exaggerated hindleg weapons, confirming the pervasive role of sexual selection in driving variation in male size and sexual dimorphism. Collectively, my research contributes to our understanding of the forces that shape the evolution of morphology in animals and their eggs

Singing Beetles? Figuring out how male rhinoceros beetles produce their courtship songs.

Insects produce sound in wildly-diverse ways, from the vibrating wings of chirping crickets to the pulsating tympanum of whining of cicadas. Beetles (order: Coleoptera) use sound in aggressive displays, alarm calls, and courtship sequences. Although all beetles appear to generate sounds using stridulation, where a plectrum, or pick, is rubbed against a pars stridens, or file, species differ in the size and location of these structures, resulting in a diverse mechanistic array of sound production within this order. The Japanese rhinoceros beetle, Trypoxylus dichotomus, was recently observed stridulating during courtship sequences; however, the mechanism of sound production, including the body parts involved and their fine structure, were unknown. I used videos of singing males, topical applications of nail polish to putative file structures, and light and scanning electron microscopy (SEM), to localize and characterize the stridulatory apparatus. Here, I show that the pars stridens is located on the inside apical tip of each elytron, and it is scraped by a plectrum located on the dorsal surface of the abdomen. By either pumping the abdomen forward and back, or swiping it side to side, males are able to produce two distinct types of acoustic signals. Future studies will explore the properties of the male courtship song and the details of female preference

Saint-Yrieix-la-Perche (Haute-Vienne). Centre-bourg

Un important programme de réaménagement du quartier de la Collégiale, visant l’ensemble de la voirie et des places périphériques (places du Moustier et Attane) a été précédé d’une complète réhabilitation des principaux collecteurs d’eaux usées et de l’adduction eau potable sous les rues et places concernées. La stratigraphie apparaît particulièrement bouleversée et difficilement interprétable, à l’exception du profil du substrat, gneissique et micaschisteux. Ce substrat se situe souvent assez..

Un champ de tumulus du Premier Age du Fer à Glandon (Haute-Vienne)

Boisseau Romain, Lambert Joël. Un champ de tumulus du Premier Age du Fer à Glandon (Haute-Vienne). In: Gallia, tome 33, fascicule 1, 1975. pp. 1-25

Overcoming mechanical adversity in extreme hindleg weapons.

The size of sexually selected weapons and their performance in battle are both critical to reproductive success, yet these traits are often in opposition. Bigger weapons make better signals. However, due to the mechanical properties of weapons as lever systems, increases in size may inhibit other metrics of performance as different components of the weapon grow out of proportion with one another. Here, using direct force measurements, we investigated the relationship between weapon size and weapon force production in two hindleg weapon systems, frog-legged beetles (Sagra femorata) and leaf-footed cactus bugs (Narnia femorata), to test for performance tradeoffs associated with increased weapon size. In male frog-legged beetles, relative force production decreased as weapon size increased. Yet, absolute force production was maintained across weapon sizes. Surprisingly, mechanical advantage was constant across weapon sizes and large weaponed males had disproportionately large leg muscles. In male leaf-footed cactus bugs, on the other hand, there was no relationship between weapon size and force production, likely reflecting the importance of their hindlegs as signals rather than force-producing structures of male-male competition. Overall, our results suggest that when weapon force production is important for reproductive success, large weaponed animals may overcome mechanical challenges by maintaining proportional lever components and investing in (potentially costly) compensatory mechanisms

Data from: Habituation in non-neural organisms: evidence from slime moulds

Learning, defined as a change in behaviour evoked by experience, has hitherto been investigated almost exclusively in multicellular neural organisms. Evidence for learning in non-neural multicellular organisms is scant and only a few unequivocal reports of learning have been described in single celled organisms. Here we demonstrate habituation, an unmistakable form of learning, in the non-neural organism Physarum polycephalum. In our experiment, using chemotaxis as the behavioural output and quinine or caffeine as the stimulus, we showed that P. polycephalum learnt to ignore quinine or caffeine when the stimuli were repeated, but responded again when the stimulus was withheld for a certain time. Our results meet the principle criteria that have been used to demonstrate habituation: responsiveness decline and spontaneous recovery. To distinguish habituation from sensory adaptation or motor fatigue, we also show stimulus specificity. Our results point to the diversity of organisms lacking neurons, which likely display a hitherto unrecognized capacity for learning, and suggest that slime moulds may be an ideal model system in which to investigate fundamental mechanisms underlying learning processes. Besides, documenting learning in non-neural organisms such as slime moulds is centrally important to a comprehensive, phylogenetic understanding of when and where in the tree of life the earliest manifestations of learning evolved

The metabolic costs of fighting and host exploitation in a seed-drilling parasitic wasp

International audienceOviposition sites may be challenging and energetically costly to access for females in the presence of competitors contesting that resource. Additionally, oviposition sites may be difficult to reach, and penetrating a hard substrate can raise energy costs. In the seed-drilling parasitic wasp Eupelmus vuilleti, females actively fight with conspecific competitors over access to hosts. They are often observed laying eggs on already parasitized hosts (superparasitism) living inside cowpea seeds despite the resulting larval competition. Using flow-through respirometry, we quantified the metabolic costs of fighting and of drilling through the seed to access the host, to understand the wasp's fighting strategies and the occurrence of superparasitism. Agonistic interactions such as kicks or pushes generated very small instantaneous costs, but the females that won their contests had higher pre-contest metabolic rates, suggesting a potential long-term cost associated with dominance. We also found that drilling holes through the seed accounted for approximately 15% of a wasp's estimated daily energy budget, and that females can reduce these drilling costs by reusing existing holes. Because exploiting new seeds incurs both drilling costs and the risk of fights, it appears cost effective in some situations for females to avoid confrontations and lay eggs in existing holes, on already parasitized hosts. Our study helps explain the evolution of superparasitism in this system

Replication Data for: Overcomic mechanical adversity in extreme hindleg weapons

Data supporting the publication "Overcoming mechanical adversity in extreme hindleg weapons", including one dataset for Sagra femorata and one dataset for Narnia femorata

Habituation in non-neural organisms: Evidence from slime moulds

Learning, defined as a change in behaviour evoked by experience, has hitherto been investigated almost exclusively in multicellular neural organisms. Evidence for learning in non-neural multicellular organisms is scant, and only a few unequivocal reports of learning have been described in single-celled organisms. Here we demonstrate habituation, an unmistakable form of learning, in the non-neural organism Physarum polycephalum. In our experiment, using chemotaxis as the behavioural output and quinine or caffeine as the stimulus, we showed that P. polycephalum learnt to ignore quinine or caffeine when the stimuli were repeated, but responded again when the stimulus was withheld for a certain time. Our results meet the principle criteria that have been used to demonstrate habituation: Responsiveness decline and spontaneous recovery. To distinguish habituation from sensory adaptation or motor fatigue, we also show stimulus specificity. Our results point to the diversity of organisms lacking neurons, which likely display a hitherto unrecognized capacity for learning, and suggest that slime moulds may be an ideal model system in which to investigate fundamental mechanisms underlying learning processes. Besides, documenting learning in non-neural organisms such as slime moulds is centrally important to a comprehensive, phylogenetic understanding of when and where in the tree of life the earliest manifestations of learning evolved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Full dataset

All variables measured are in this table