Drosophila grimshawi

Magnacca, Karl N., Foote, David & O’Grady, Patrick M., 2008, A review of the endemic Hawaiian Drosophilidae and their host plants, Zootaxa 1728, pp. 1-58 : 27-28

grimshawi clade

With 77 species, the grimshawi clade accounts for the bulk of picture wing species. It is also the most diverse in host usage, comparable to the modified mouthparts clade. On a finer scale, however, more specificity emerges. Within each species subgroup, a relatively small number of host shifts appears to have taken place ( Table 5; to avoid confusion with the larger clade, their “ grimshawi subgroup” is referred to here as the crucigera subgroup). For example, 12 of the 17 orphnopeza subgroup species are from either Agavaceae or Araliaceae , including one oligophagous species that uses both; species of the vesciseta subgroup use only Amaranthaceae , Nyctaginaceae , or Urticaceae ; the odontophallus subgroup is exclusively on Agavaceae ; and monophagous species of the crucigera subgroup use only Pandanaceae or Thymelaeaceae . The low overlap in host families between subgroups implies that specialization on a host plant may have played a major role in the early diversification of the picture wing clade. This is in contrast to the AMC clade, where little hostswitching has taken place across the whole group, and the modified mouthparts group, where the dissita and quadrisetae subgroups show no clear pattern of host usage. The lack of a detailed species-level phylogeny such as exists for the planitibia group ( Bonacum, et al., 2005), and numerous confounding shifts to rarer hosts such as Nyctaginaceae and Sapindaceae , preclude further speculation on evolution of host usage among the grimshawi subgroups.

species complex a data species

ecological

with polyphagous y n Agavaceae Amaranthaceae Araliaceae Fabaceae Myoporaceae Nyctaginaceae Pandanaceae Sapindaceae Thymelaeaceae Urticaceae / oligophagous

crucigera 8 1 3 2 3 hawaiiensis 9 5 3 3 1 2 odontophallus 4 4 orphnopeza 17 2 2 9 1 1 1 3 punalua 5 3 1 2 1 1 vesciseta 11 5 5 2 3 1

a The discreta and distinguenda subgroups are not shown since rearing data is only available for one species from each.

Despite the wide diversity of host families used by the grimshawi clade, the only substrate shift has been from stems and bark proper to sap flux in the hawaiiensis subgroup. The latter is a similar habitat that is sometimes used by other picture wing species, particularly in the orphnopeza subgroup. Only two species commonly use other substrate types: D. punalua will sometimes use the fruit and leaves of Freycinetia in addition to the stems, and D. crucigera , a highly polyphagous species, will also use fruit.

The most striking aspect of the breeding records for the grimshawi clade is not so much the variety of host families that are used, as one that is not: Campanulaceae . This is considered one of the most important hosts for Hawaiian drosophilids in general, but especially for the other clades ( adiastola and planitibia ) in the picture wing group. Yet there are almost no records for the family in the grimshawi clade; in addition to four polyphagous species ( D. crucigera , D. disjuncta , D. grimshawi , and D. villosipedis ), there are only 4 records from 2 species ( D. limitata and D. murphyi ), and even these may be incidental. The near-absence of such a significant host from this large, highly host-variable group is remarkable, and warrants further investigation.

Araliaceae , particularly the genus Cheirodendron , is another very common host plant for Hawaiian Drosophilidae . While there are several records of grimshawi clade species using Araliaceae , nearly all are confined to the orphnopeza subgroup, the same 4 polyphagous species mentioned above, and scattered incidental records. Of those species that do use Araliaceae , 80% have been reared from either Tetraplasandra or Reynoldsia (see Appendix 1), often in lowland and/or relatively dry habitats. In contrast, none of the 240 Araliaceae records from the AMC and modified mouthparts clades are from Reynoldsia and only 22 (9%) are from Tetraplasandra , and all but one are from montane wet locations.

In general, the species of the grimshawi clade tend to favor more mesic to dry forest plants: Acacia , Charpentiera , Myoporum , Pisonia , Pleomele , Reynoldsia , Sapindus , Tetraplasandra , Urera , and Wikstroemia . Although many of these live in wet forest as well, it appears likely that the grimshawi clade evolved as a mesic assemblage, perhaps as sister to the nudidrosophila and ateledrosophila groups. It is perhaps not so surprising then that the characteristic plants of the wet forest – Cheirodendron , Clermontia , and Cyanea – are lacking from their diet, especially when these plants are already heavily utilized by other picture wings.