High incidence and correlates of dioecy in the flora of the Canadian Arctic Archipelago

Abstract

In comparing the incidence of dioecy in North American floras, we report a strong, positive correlation with increasing latitude. Dioecy in the High Arctic is highly correlated with woodiness, as elsewhere. It is significantly correlated with fleshy, zoochorous fruits as well documented elsewhere. Correlation with floral inconspicuousness, which we define in terms of attractiveness to pollinators (i.e., functionality to pollination), is weak and statistically insignificant. Published findings on that correlation are equivocal; different authors variously defined inconspicuousness in ways that may or may not reflect functionality in pollination. Although we acknowledge that for some diverse taxa (e.g., Salix spp.) the relative importances of anemophily, zoophily (entomophily), and ambophily are unknown, we assigned species to (a) anemophily if evidence for entomophily could not be invoked and (b) entomophily if insect pollination was considered possible (i.e., counts for entomophily include possibly ambophilous species). We found no correlation between dioecy and anemophily/entomophily. The view that insularity favours establishment of dioecious taxa may be invoked by considering localized and disjoint post-glacial colonization. The view that dioecy, as a form of xenogamy, has evolved in response to offsetting the adverse consequences of inbreeding and accumulation of mutations may apply under High Arctic conditions, further eroding ideas that short, harsh, active seasons promote self-fertilization (autogamy), agamospermy, and vegetative reproduction while disfavouring xenogamy by insect or wind pollination.

Keywords

• plant sexual reproduction
• latitudinal gradient
• pollination
• anemophily
• floral characters
• fleshy fruit
• woodiness