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Influence of environmental factors on wing polymorphism of ...

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c<strong>on</strong>necti<strong>on</strong> between <strong>wing</strong> morph and type <str<strong>on</strong>g>of</str<strong>on</strong>g> habitat in Nearctic water striders,with effect <str<strong>on</strong>g>of</str<strong>on</strong>g> temperature, photoperiod and genetic mechanism in some species.In general, both genetic and <str<strong>on</strong>g>envir<strong>on</strong>mental</str<strong>on</strong>g> <str<strong>on</strong>g>factors</str<strong>on</strong>g> during egg and larvaldevelopment are thought to affect <strong>wing</strong> dimorphism in gerrids, as previouslyassumed by (BRINKHURST, 1959). Most important <str<strong>on</strong>g>envir<strong>on</strong>mental</str<strong>on</strong>g> <str<strong>on</strong>g>factors</str<strong>on</strong>g>c<strong>on</strong>sidered are temperature and photoperiod, causing low proporti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g>macropterous morph in summer generati<strong>on</strong>. More l<strong>on</strong>g-<strong>wing</strong>ed specimens thusoccur in overwintering generati<strong>on</strong>. Possibility to leave unfavorable habitat is alsoclear advantage. High proporti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> macropterous individuals can thus besupposed in inhospitable or unstable habitats. Ephemeral habitat (drying out)should be recognized by increased temperature, populati<strong>on</strong> density and probablyalso by food shortage (see MURAJI et al., 1989).Laboratory experimentsThe genetic c<strong>on</strong>trol and effect <str<strong>on</strong>g>of</str<strong>on</strong>g> five <str<strong>on</strong>g>envir<strong>on</strong>mental</str<strong>on</strong>g> c<strong>on</strong>diti<strong>on</strong>s (photoperiod,temperature, populati<strong>on</strong> density, food availability and drying out <str<strong>on</strong>g>of</str<strong>on</strong>g> the habitat =rearing <strong>on</strong> wet filtrate paper) <strong>on</strong> <strong>wing</strong> <strong>polymorphism</strong> has been tested ingerromorphan bugs. We found results for 15 gerromorphan bugs (eight Gerridae,five Veliidae and two Mesoveliidae). Am<strong>on</strong>g these species, nine were tested forpopulati<strong>on</strong> density (five positive (DITRICH & PAPÁČEK, 2009b; HARADA et al.,1997; MURAJI et al., 1989; MURAJI & NAKASUJI, 1988), three n<strong>on</strong>e (DITRICH &PAPÁČEK, 2009b; HARADA & SPENCE, 2000) and <strong>on</strong>e negative effect (HARADA &SPENCE, 2000) <strong>on</strong> development <str<strong>on</strong>g>of</str<strong>on</strong>g> MP specimens. Effect <str<strong>on</strong>g>of</str<strong>on</strong>g> photoperiod wasproved in six (ANDERSEN, 1982; BLANCKENHORN & FAIRBAIRN, 1995; INOUE &HARADA, 1997; MURAJI et al., 1989; VEPSÄLÄINEn, 1974; ZERA et al., 1983) out <str<strong>on</strong>g>of</str<strong>on</strong>g>eight species tested (zero effect: ANDERSEN, 1982; DITRICH & PAPÁČEK, 2009a),effect <str<strong>on</strong>g>of</str<strong>on</strong>g> temperature in three (HARADA, 1992; MURAJI et al., 1989; PFENNING etal., 2008; VEPSÄLÄINEN, 1974) out <str<strong>on</strong>g>of</str<strong>on</strong>g> six species (zero effect: DITRICH & PAPÁČEK,2009a; SPENCE & ANDERSEN, 1994). Wing development was not affected byhabitat desiccati<strong>on</strong> in both species tested (DITRICH & PAPÁČEK, 2009a; KISHI etal., 2002). Increased food availability increased a proporti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> macropters inMicrovelia douglasi (MURAJI et al., 1989). Genetic mechanisms were found inthree (AHLROTH et al., 1999; SPENCE, 1989; ZERA et al., 1983) out <str<strong>on</strong>g>of</str<strong>on</strong>g> five speciestested (zero effect: ANDERSEN, 1982; FAIRBAIRN, 1988).C<strong>on</strong>clusi<strong>on</strong>According to field observati<strong>on</strong>s, <strong>wing</strong> <strong>polymorphism</strong> is at least partiallyc<strong>on</strong>trolled by <str<strong>on</strong>g>envir<strong>on</strong>mental</str<strong>on</strong>g> c<strong>on</strong>diti<strong>on</strong>s in most species. The most significant<str<strong>on</strong>g>factors</str<strong>on</strong>g> are photoperiod and temperature (seas<strong>on</strong>al, eventually latitudinal<strong>polymorphism</strong>) and temperature, populati<strong>on</strong> density, food shortage andsubstrate desiccati<strong>on</strong> during larval development (when needed to leaveunfavorable or drying habitat). Temperature thus seems to have crucial effect <strong>on</strong><strong>wing</strong> <strong>polymorphism</strong>. Laboratory experiments have validated the photoperiodeffect in most cases, and the change in <strong>wing</strong> morphs proporti<strong>on</strong>s followed lifehistory <str<strong>on</strong>g>of</str<strong>on</strong>g> particular species. However, the effect <str<strong>on</strong>g>of</str<strong>on</strong>g> temperature was studied infew species <strong>on</strong>ly and the results were not c<strong>on</strong>vincing - the effect <str<strong>on</strong>g>of</str<strong>on</strong>g> temperaturewas found <strong>on</strong>ly in a half <str<strong>on</strong>g>of</str<strong>on</strong>g> species. Some species differed in their resp<strong>on</strong>se toincreased populati<strong>on</strong> density when usually more macropterous individuals17

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