Mechanical vs. Beetle-mediated Self-pollination in Gossypium Tomentosum (Malvaceae), an Endangered Shrub

Abstract

Experimental hand pollinations of the endangered, Hawaiian, endemic, Gossypium tomentosum Nutt. Ex. (Malvaceae) showed that it was self-compatible, but self-pollination resulted in reduced reproductive output. Field observations and pollen tube analyses using fluorescence microscopy showed that mechanical self-pollination in this species included a mechanism known as bending stigmas. A receptive stigma bent backwards and contacted dehiscent anthers in 7% of flowers found on 17 G. tomentosum plants. The yellow flowers were nectarless and were not visited by most anthophilous insects in situ except for the introduced, nitidulid beetle, Aethina concolor Macleay. Collections and insect GI-tract dissections showed that A. concolor carried and ate the pollen of the host flower. Field observations recorded regular contact between beetles and stigma lobes as these insects exited the flowers effecting selfpollination. Behavioral experiments showed that the beetles responded positively to a yellow visual cue. Under some circumstances, an introduced pollen vector may help maintain a low level of reproductive success in an insular endemic.

Assessment of Persistence of Hybrids between Alien Pima Cotton,Gossypium barbadense(Malvaceae), and Endemic Hawaiian Cotton,G. tomentosum, in Hawai'i1

“…The three species have shared habitat preferences (Wagner et al 1999) and insect pollinators (Krakos et al 2010, Pleasants and and are known to be interfertile (Meyer and Meyer 1961, Stephens 1964, DeJoode and Wendel 1992. In addition, all three species are capable of outcrossing; both alien cotton species are facultative selfpollinators and opportunistic outcrossers (Oosterhuis and Jernstedt 1999), and Hawaiian cotton primarily outcrosses (Krakos et al 2010). For these reasons, Daehler and Carino (2001) suggested that alien and native cotton species may hybridize and spread in the Hawaiian Islands.…”

“…comm.). With sufficient rainfall, Gossypium tomentosum produces flowers throughout the year (Stephens 1964), which are viable for a single day (Krakos et al 2010). Though selfcompatible, pollen tube formation is more vigorous when cross-pollinated, a mechanism that is facilitated by the extended style of the native cotton (Krakos et al 2010).…”