Morphological variation in the forelegs of the Hawaiian Drosophilidae. I. The AMC clade

Abstract

The Hawaiian Drosophilidae possess spectacular diversity in male foreleg modifications, many of which are unknown in other Diptera. The greatest diversity in foreleg morphology is in the antopocerus, modified tarsus, and ciliated tarsus clade (AMC Clade), a group of 95 species. The modified tarsus flies are divided into the bristle, ciliated, split, and spoon tarsus subgroups. The bristle tarsus species feature one or two rows of thickened setae on the basitarsus. The split tarsus species are characterized by only having four tarsal segments, in contrast to five tarsomeres in the remainder of Diptera. Based on comparisons of the apparent ground state of ventral setal rows across the Hawaiian Drosophila, we suggest that it is the second tarsal segment which has been lost. The spoon tarsus species are characterized by having the second tarsomere modified into a setae-filled, concave-shaped spoon. The ciliated tarsus species, all of which possess one or more elongate setae on the tarsus of males, are probably not monophyletic with respect to the bristle tarsus subgroup. The antopocerus flies are characterized by a long basitarsus, with extensive setation on the tibia and basitarsus of some species. The use of these foreleg modifications in courtship behavior has been previously described and it is suggested that they represent the results of sexual selection. The current work expands on previous morphological analyses, presenting a level of detail not previously possible without SEM images. The new characters revealed will figure prominently in future cladistic studies.

Ultrastructural variation and adaptive evolution of the ovipositor in the endemic Hawaiian Drosophilidae

“…Members of this group defined by morphological modifications of the male foreleg are much smaller flies, but phylogenetically closely related to the antopocerus species group (Lapoint, Magnacca, & O'Grady, ; Stark & O'Grady, ), being clustered into the AMC clade (the antopocerus , modified tarsus and ciliated tarsus groups). Thus, it is not surprising that D. waddingtoni , a representative of the spoon tarsus subgroup of modified tarsi flies, has an ovipositor that is similar in form when viewed laterally (Figure e) and ventrally to that of members of the antopocerus group (Figures c,f and a–d).…”

Hawaiian Drosophila as an Evolutionary Model Clade: Days of Future Past

“…The Hawaiian Drosophila also inhabit incredibly broad ecological niches on the islands and rely on broad ranges of host plants for survival. [22][23][24][25] This general statement about variation holds for comparisons between islands, as well as differences between volcanoes comprising the same island. Several recent studies address variation and the search for natural selection in Hawaiian Drosophilidae (mostly picture wing flies).…”

“…[12,13,67] One study examined the ecology of oviposition of a sibling species pair -D. heedi and D. silvarentis [68] and demonstrated microhabitat differentiation of their egg laying sites. Expansion of host plant descriptions for the group was accomplished [22] and a relatively complete view of [25,74] www.advancedsciencenews.com www.bioessays-journal.com this ecological parameter for the majority of named species now exists. Having this ecological context allows for broader tests of evolutionary hypotheses about adaptation and coevolution of the flies and their host plants.…”

Evolving doublesex expression correlates with the origin and diversification of male sexual ornaments in the Drosophila immigrans species group

“…The forelegs of true flies (Diptera) often show dramatic male‐specific modifications (Daugeron, Plant, Winkler, Stark, & Baylac, ; Eberhard, ; Hardy, ; Ingram, Laamanen, Puniamoorthy, & Meier, ; Sivinski, ; Stark & O'Grady, ). Structures composed of modified bristles are especially common and have evolved independently in many Dipteran lineages.…”

“…Structures composed of modified bristles are especially common and have evolved independently in many Dipteran lineages. In the family Drosophilidae alone, examples include a variety of bristle brushes and bristle‐filled spoon structures in Hawaiian Drosophila (Stark & O'Grady, ), pincushion‐like outgrowths covered with fine bristles in Zaprionus (Chassagnard & Tsacas, ; Tsacas & Chassagnard, ), the thick, often massive “sex combs” in the Drosophila melanogaster and obscura species groups (Hanna‐Alava, ; Kopp, ), and the densely packed bristle brush in Drosophila immigrans (Sturtevant, ) and its relatives (Figure ). Repeated origin of male‐specific bristle modifications in the same body region (most commonly, the tarsi of the front legs) suggests that across Diptera, the forelegs have been a target of sexual selection.…”