Host plants, fitness and developmental instability in a guild of cactophilic species of the genus Drosophila

ESTEBAN HASSON ; IGNACIO M SOTO; VALERIA P CARREIRA; CRISTIAN CORIO; EDUARDO M SOTO; MARÍA IL BETTI

Ecotoxicology Research Developments

Nova Science Publishers

Lugar: Hauppauge NY; Año: 2009; p. 89 - 109

Cactophilic Drosophila, fruit flies that feed and breed in the necrotic tissues ofCactaceae, are excellent models to investigate adaptation to a relatively narrowspectrum of potential host plants. Cactus hosts may be, in principle, classified in twowide classes consisting of prickly pears (genus Opuntia) and columnar cacti which interms of their chemistry represent environments that may constitute different types ofchallenges to the growing larvae. In this sense, columnar cacti are known to haveseveral types of toxic compounds such as alkaloids, terpenoids, atypical fatty acidswhich may be stressful for the flies. In the last few years we have studied differentaspects of flies´ performance in their natural breeding sites in two pairs of cactophilicsibling species inhabiting South American arid lands. First, we studied the pair D.koepferae and D. buzzatii. Though, these two species have a certain degree of nicheoverlap, the former breeds and feeds preferentially in the decaying tissues of columnarsof the genera Trichocereus and Cereus, while the latter, utilizes prickly pears (genusOpuntia). Overall, our results showed that in both species fitness related traits (survival,developmental time and wing morphology) are dramatically affected by the cactus host.Survival probability, developmental time and wing size were maximized when flies ofboth species were reared in the primary host of D. buzzatii (O. sulphurea), while theopposite occurred in the primary host of D. koepferae (T. terschekii). The second set ofstudies investigated the response of another pair of sibling species, D. gouveai and D.antonietae (whose niches are completely disjunct) when reared in their natural hosts.Our results also revealed a remarkable effect of the host plant on survival,developmental time and wing morphology. Indeed, survival probability was increased,development substantially reduced and wing size increased in the primary host of D.gouveai (Pilosocereus machrisii) in both species, while the reverse was true in the hostof D. antonietae (Cereus hildmannianus). In addition, we measured fluctuatingasymmetry (FA, random differences in the morphology of a bilateral organ) as anindicator of developmental instability in both pairs of species in their preferred andunpreferred cactus hosts. In these experiments we detected an increased level ofdevelopmental instability (greater FA in wing size) in flies of both species reared intheir respective secondary host. Future research directions point to, on one hand, to thecharacterization of the genetic basis of the differential responses observed in both pairsof species to their respective rearing hosts, and, on the other hand, to the identificationof the chemical compounds effecting these responses.