Interactions between hawkmoths and flowering plants in East Africa: polyphagy and evolutionary specialization in an ecological context

Abstract

Hawkmoths (Lepidoptera, Sphingidae) are considered important pollinators in tropical regions, but the frequency and degree of reciprocal specialization of interactions between hawkmoths and flowers remain poorly understood. Detailed observations at two sites in Kenya over a two‐year period indicate that adult hawkmoths are routinely polyphagous and opportunistic, regardless of their proboscis length. About 700 individuals of 13 hawkmoth species were observed visiting a wide range of plant species at the study sites, including 25 taxa that appear to be specifically adapted for pollination by hawkmoths. We estimate that 277 plant species in Kenya (c. 4.61% of the total angiosperm flora) are adapted for pollination by hawkmoths. Floral tube lengths of these plants have a bimodal distribution, reflecting the existence of two hawkmoth guilds differing in tongue length. Hawkmoths exhibited strongly crepuscular foraging patterns with activity confined to a 20‐min period at dusk and, in some cases, a similar period just before dawn. Corolla tube length appears to act as a mechanical filter as the longest‐tubed plants were visited by the fewest hawkmoth species and these were exclusively from the long‐tongued guild. Tube length showed a strong positive relationship with nectar volume, even after phylogenetic correction, which implies that plants with long corolla tubes are under selection to offer relatively large amounts of nectar to entice visits by polyphagous long‐tongued hawkmoths. Our study shows that diffusely co‐evolved pollination systems involving long‐tongued hawkmoths are clearly asymmetrical, with plants exhibiting a high degree of floral specialization, while hawkmoths exhibit polyphagous behaviour. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 199–213.

Butterfly Pollination of the Dryland Wildflower Gloriosa minor

“…Observations made during this study support the butterfly pollination syndrome for this species (psychophily) and are consistent with those made for other butterflypollinated species in Africa, including both the nectar production and patterns of anthesis (Johnson, 1992;Johnson & Bond, 1994). This study adds to our knowledge of butterfly-pollination in East Africa, as previous work has only shown limited involvement of skipper butterflies in papaya pollination (Martins & Johnson, 2009), and the main specialised lepidopteran pollinators documented in East Africa are primarily hawkmoths (Sphingidae) (Martins & Johnson, 2007;2009;2013). Observations of Combretum rotundifolium Rich., Cadaba sp.…”

Beyond neutral and forbidden links: morphological matches and the assembly of mutualistic hawkmoth–plant networks

“…; Haber & Frankie ; Hougen‐Eitzman & Rausher ; Agosta & Janzen ; Moré et al . ; Martins & Johnson ). Here, we analysed the role of the neutral, forbidden links and morphological match hypotheses in structuring mutualistic hawkmoth–plant networks.…”

Pollination in Lilium sargentiae (Liliaceae) and the first confirmation of long‐tongued hawkmoths as a pollinator niche in Asia

“…convolvuli is common in many countries in the Old World (Pittaway & Kitching, ). A guild of plant species in Africa has evolutionarily converged for pollination by long‐tongued hawkmoths and A. convolvuli was found to be the dominant or sole pollinator of those species (Martins & Johnson, ; Johnson & Raguso, ). Since the geographical distribution of pollinators is important for biogeographical patterns of floral evolution (Stebbins, ) and A. convolvuli is not confined to Africa, the pollinator niche of long‐tongued hawkmoths is also supposed to occur and to be used by plants elsewhere, some of which may also have evolved to specialize on A. convolvuli and other hawkmoths similar in tongue length.…”