Peter O'Byrne wrote: >Things do not look good for the "one orchid species, one insect species" >hypothesis.
Indeed. But two points that you may have elided: 1: The complexity / zygomorphy / whatever of the orchid flower is not un caprice de dieu, but something that is actively evolving under insect control. Ergo, how it looks at microscopic detail matters to insects. I suspect that the flower at least sometimes and to a degree "imprints" the pollinator - in effect, says 'was it good for you too? Well, go and find another just like me'. THis, because the pollinia system means that all of the gametes are bound up in one (all right, up to eight) package(s), but in effect the flower gets just one shot. Other insect pollinators tend to have dusty pollen, many anthers, lots of bites at the bug's cherry. Orchids are less of a shotgun, more a precise sniper rifle and they get just one shot. It has to hit its target first time, which means that the insect in question has to be sent on a quest through the forest. My point: floral form may be a self-driving evolutionary isolation barrier, operating through insect 'psychology'. 2: Two clades diverge by many small steps, and what looks like a huge phenotypic change may be a point mutation in a e.g. homeobox gene. However, what makes for evolutionary isolation or inclusion is always the phenotype. Thus one could have a swarm - Arundina - building clade-potential but still apparently interbreeding, despite being anything from a harebell to a hollyhock in appearance, whilst others may be separated by a single whisker or callus. Coelogyne, for example - the Clayton book shows many species which are all-but identical but which apparently operate in sexual isolation, perhaps due to allopatry - with all of the problems that you mention - with changed time of flowering (in my view, an undervalued variant in seasonal regions) or perhaps due to sensitivities amongst our friends, the bugs; as (1). One should note that "isolation" is anyway a statistical rather than a binary concept. If the chances of reproduction between interbreeding set A and set B are 80% of the rate of breeding within the set, then the progeny will always be fewer than those of either A or B, and thus at a major disadvantage. This could be offset by hybrid vigor, perhaps, but not always; particularly if A and B are closely related and have much the same recessive burden. . _____________________________________ Oliver Sparrow Tel: UK (0)20 7736 9716 www.chforum.org www.treknepal.org www.datafreeze.com
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