Physiological plasticity in arthropods from Marion Island : indigenous and alien species

[摘要] ENGLISH ABSTRACT:Climate sets range limits in many taxa, and as climate changes, the ranges that plants andanimals occupy are altered. The responses of species to climate change involve eithermigration or local adaptation. An investigation of the local physiological adaptationshown by indigenous and alien arthropods to temperature acclimation formed the primaryfocus of this study. Increased environmental temperatures favour the establishment ofalien species on Southern Ocean Islands. The first records of Porce/lio scaber Latreille,1804 (Isopoda, Porcellionidae) and an Aphidius wasp species from Marion Island weredocumented here. The alien wasp was discovered in 2003 and had a current knowndistribution along the east coast of Marion Island. Both isopods and wasps werereproducing successfully on Marion Island. The wasp species is an aphid parasitoid andhad been found mummifying the alien aphid Rhopalosiphum padi. These introductionshighlighted the ongoing conflict between use and conservation on the Southern OceanIslands.Despite considerable work on the upper and lower lethal limits of insects, several majortaxa have received little attention. Here this issue was addressed and the lower and upperthermal tolerances and cold hardiness strategy of Antarciopsocus jeanneli Badonnel(Psocoptera: Elipsocidae) from sub-Antarctic Marion Island was investigated. A.jeanneli is freeze intolerant, and more specifically, moderately chill tolerant. Field freshA. jeanne li had a mean supercooling point (SCP) of -11.1oC, whereas LTSO was -7.7°C,indicating pre-freeze mortality. A. jeanneli responded to acclimation: mean SCPincreased from -IS.8°C at a treatment temperature ofO°C, to -7.3°C at ISOC.Investigations of the responses to acclimation of upper and lower lethal limits and limitsto activity in insects have focussed primarily on Drosophila. Halmaeusa atriceps(Staphylinidae) was examined for thermal tolerance responses to acclimation, andseasonal acclimatization. In summer and winter, lower lethal temperatures of adults andlarvae were c. -7.6 ± 0.03 and -11.1 ± 0.06 °C, respectively. Supercooling points (SCPs)were more variable, with winter SCPs of -S.4 ± 0.4 °C in larvae and -6.3 ± 0.8 °C inadults. The species appeared to be chill susceptible in summer and moderately freezetolerant in winter, thus showing seasonal acclimatization. Critical thermal minima variedbetween -3.6 ± 0.2 and -0.6 ± 0.2 °C in larvae, and from -4.1 ± 0.1 to -0.8 ± 0.2 °C inadults. These findings were in keeping with the general pattern found in insects, althoughthis species differed in several respects from others found on Marion Island.In this study the differential responses of indigenous and invasive springtails totemperature were explicitly examined in the context of the beneficial acclimationhypothesis (BAH) and its alternatives. In particular, the thermal acclimation responses ofdesiccation resistance, supercooling ability, lower and upper thermal limits werecompared. Invasive springtails (Pogonognathellus jlavescens, Isotomurus palustris andCeratophysella denticulata) did not display greater phenotypic flexibility than indigenousspringtails (Cryptopygus antarcticus and Tullbergia bisetosa), but did perform betterunder high temperature conditions. Indigenous species, however, performed better underlow temperature conditions. In most cases the BAH was not supported, or could not bedistinguished from its alternatives. The prediction that invasive species will outperformindigenous species as climates on Southern Ocean Islands warm was supported.Because temperature plays such a large role in the distribution, abundance andphysiological tolerances of invertebrates, microhabitat temperatures along an altitudinalgradient (0 to 800 m above sea level (asi)) were investigated over a two-year period onMarion Island. Mean microhabitat temperatures were comparable to those from previousstudies for Southern Ocean Islands, and declined with increasing altitude. The 800 m aslsite had the most severe microclimate (highest absolute maximum, lowest absoluteminimum and the highest frequency of freeze-thaw cycles). Year one was substantiallycolder than year two, indicating that interannual variation in microclimate conditionscould be responsible for substantial mortality amongst. invertebrate populations. Indeed,indigenous species were best able to tolerate the high incidence of low temperatures athigh altitudes, whereas alien species appeared to be confined to lower altitudinal sites onMarion Island, possibly as a consequence of extreme low temperatures at higher altitudes.

[发布机构] Stellenbosch University