Introduction

That [bees] and other insects, while pursuing their food in the flowers, at the same time fertilize them without intending and knowing it and thereby lay the foundation for their own and their offspring's future preservation, appears to me to be one of the most admirable arrangements of nature.

Sprengel [1]

Although Sprengel, writing in 1793, may not have recognized the evolutionary implications of his life's work on plant-pollinator interactions, he was among the first to relate the morphological features of flowering plants to those of nectar-feeding animals. Indeed, the early evolution and diversification of angiosperms have frequently been attributed to an "arrangement" between plants and their pollinators, but how "admirable" such relationships often are remains questionable [2]. Darwin postulated that extended corollas of certain flowers represent the outcome of an evolutionary arms race between plants and their pollinators [3], with plants evolving to match, in depth, mouthpart lengths of pollinating taxa [4-7]. Consequently, the rise of flowering plants in the late Cretaceous also corresponded with a period of rapid diversification in insect feeding strategies, including the evolution of the famously elongate mouthparts associated with nectar feeding in certain Lepidoptera, Diptera, and Hymenoptera [8,9].

Although many nectar-feeding insects consume floral nectars with short mouth-parts, the benefits nectar feeders derive from their long proboscides are clear: exclusive access to deep flowers, providing copious amounts of nectar [10-13]. In fact, long-proboscid insects are able to capitalize on a wider diversity of resources than their short-proboscid counterparts as they frequent any flowers from which they can physically extract nectar whether deep or shallow [11,14-16]. Such advantages lead to the fundamental questions: Do insect nectarivores incur a cost to having such long mouthparts? If so, how can we measure these costs? What are the functional requirements of elongate mouthparts and how might they influence pollinator behavior? Clearly, a long proboscis can be unwieldy [17,18]; the control, extension, and retraction of the proboscis requires specialized machinery [19-23], and imbibement of a viscous fluid through such a slender duct entails a whole other set of biome-chanical problems [24-26]. The goal of the present chapter is to examine the functional morphology and biomechanics of nectar feeding with elongate mouthparts and to explore how physical constraints may have shaped feeding ecology and plant-pollinator relationships over evolutionary time.

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