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Most studies of phenotypic selection do not estimate selection or fitness surfaces for multiple components of fitness within a unified statistical framework. This makes it difficult or impossible to assess how selection operates on traits through variation in multiple components of fitness. We describe a new generation of aster models that can evaluate phenotypic selection by accounting for timing of life-history transitions and their effect on population growth rate, in addition to survival and reproductive output. We use this approach to estimate selection on body size and development time for a field population of the herbivorous insect, Manduca sexta (Lepidoptera: Sphingidae). Estimated fitness surfaces revealed strong and significant directional selection favoring both larger adult size (via effects on egg counts) and more rapid rates of early larval development (via effects on larval survival). Incorporating the timing of reproduction and its influence on population growth rate into the analysis resulted in larger values for size in early larval development at which fitness is maximized, and weaker selection on size in early larval development. These results illustrate how the interplay of different components of fitness can influence selection on size and development time. This integrated modeling framework can be readily applied to studies of phenotypic selection via multiple fitness components in other systems., (© 2015 The Author(s). Evolution © 2015 The Society for the Study of Evolution.)

The reproductive success of herbivorous insects largely depends on the mother's oviposition preference. In nocturnal insects, olfaction is arguably the most important sensory modality mediating mate finding, foraging, and host location. In most habitats, gravid females select among a number of plants of varying suitability, yet assessment of the neuroethological mechanisms underlying odor-guided choice between host plants is rare. Using a series of behavioral, electrophysiological, and chromatographic analyses in the Hawk moth, Manduca sexta, we show that gravid females perform a hierarchical choice among host plants of different species and qualities using olfactory cues. Both relevant plant species and qualities can be distinguished by volatile profiles collected from the headspace of these plants, and olfactory sensilla on female antennae detect more than half of the about 120 analytically detected volatiles in host plant headspace samples. Although olfactory sensory neurons present in antennal sensilla are mainly broadly tuned to multiple host compounds, some sensilla exhibit species and condition-specific responses. In fact, species and quality can be distinguished by the physiologically active components alone. Our findings thus suggest that distinguishing characteristics of both host species and quality are already represented at the sensory periphery.

Antennal lobes of adult male and female Manduca sexta were compared in order to investigate the nature and extent of sexual dimorphism of the primary olfactory center of this lepidopteran species. Complete identification of the glomeruli led to the conclusion that all female glomeruli have homologous male counterparts. Thus, there is no sex-specific glomerulus present in one sex and absent in the other. Sexual dimorphism (i.e. glomeruli present but morphologically different in males and females), however, does occur in the three glomeruli composing the male macroglomerular complex. The female homologs of this complex consist of two previously identified 'large female glomeruli' and one newly identified normal-sized glomerulus. The lateral and medial large female glomeruli are interpreted to be homologous to the first two macroglomerular-complex glomeruli-the cumulus and toroid 1. The third male component, the toroid 2, was tentatively identified with a normal-sized spheroidal glomerulus of the female, called here the 'small female glomerulus'. The 60 'ordinary' glomeruli that make up the rest of the glomerular neuropil were found to be homologous in males and females, with the exception of two anomalous (or uncertain) glomeruli. Some variations in relative position and size observed among those glomeruli suggest a diffuse, quantitative kind of sexual dimorphism.

The central projections of olfactory receptor cells associated with two distinct types of antennal sensilla in the sphinx moth Manduca sexta were revealed by anterograde staining. In both sexes, receptor axons that arise from sexually isomorphic, type-II trichoid sensilla (and possibly some basiconic sensilla) project to the spheroidal glomeruli in the ipsilateral antennal lobe. Each axon terminates in one glomerulus. Axons from a limited region of the antenna project to glomeruli throughout the lobe, arguing against strict topographic mapping of antennal receptor cells onto the array of glomeruli. Axons of sex-pheromone-selective receptor cells in the male-specific type-I trichoid sensilla project exclusively to the sexually dimorphic macroglomerular complex (MGC). Axons from sensilla on the dorsal surface of the antenna are biased toward the medial MGC and those from ventral sensilla, toward the lateral MGC. Some receptor-cell axons branch before reaching the MGC, but their terminals are always confined to one of the two main glomerular divisions of the MGC, the cumulus and toroid. These findings confirm that primary-afferent information about pheromonal and non-pheromonal odors is segregated in the antennal lobe and suggest that there is a functional correspondence between particular olfactory receptor cells and specific glomeruli.