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Male-male competition in plants is thought to exert selection on flower morphology and on the temporal presentation of pollen. Theory suggests that a plant's pollen dosing strategy should evolve to match the abundance and pollen transfer efficiency of its pollinators. Simultaneous pollen presentation should be favored when pollinators are infrequent or efficient at delivering the pollen they remove, whereas gradual dosing should optimize delivery by frequent and wasteful pollinators. Among Penstemon and Keckiella species, anthers vary in ways that affect pollen release, and the morphology of dried anthers reliably indicates how they dispense pollen. In these genera, hummingbird pollination has evolved repeatedly from hymenopteran pollination. Pollen production does not change with evolutionary shifts between pollinators. We show that after we control for phylogeny, hymenopteran-adapted species present their pollen more gradually than hummingbird-adapted relatives. In a species pair that seemed to defy the pattern, the rhythm of anther maturation produced an equivalent dosing effect. These results accord with previous findings that hummingbirds can be more efficient than bees at delivering pollen.

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The abundance and distribution of 21 species of euphausids collected in surface waters (0-200 m) at 69 stations of the Gulf of Mexico and the Yucatan Shelf was analyzed. Zooplankton samples were taken during the JS8601 cruise on board the R/V "Justo Sierra" of the UNAM, in April-May, 1986. During this survey mesoscale hydrographic features such as anticyclonic and cyclonic gyres, and upwelling, were detected in the area. The most abundant species was Stylocheiron carinatum (29.86%), followed by Euphausia tenera (19.97%) and S. suhmi (15.18%). Species richness increased at night: densities were 3.07 times higher then. Apparently, the migratory behaviour, of euphausids buffered the expected effect of the mesoscale features in the local euphausid community. The Bray-Curtis Index revealed three clusters of stations. The first one represented the influence of coastal and shelf waters on the euphausid community. The second group is a mixed oceanic-shelf community, and the third one was related to the Gulf oligotrophic oceanic waters. A fourth group included shallow areas in which no euphausids occurred. The relatively poor anticyclonic eddies did not influence the local euphausid community although low euphausid densities were expected. The relatively richer features, the cyclones, showed higher average densities. Euphausid densities related to the influence of upwelling areas showed density values similar to those recorded in the anticyclones. Two species (S. suhmi and S. carinatum) occurred in all the Gulf of Mexico regardless of the mesoscale environments or the time of day. L'abondance et la repartition de 21 especes d'Euphausiaces recoltes dans les eaux de surface (0-200 m) sur 69 stations du Golfe du Mexique et du plateau du Yucatan ont ete analysees. Les echantillons de zooplancton ont ete preleves au cours de la campagne JS8601 a bord du R/V "Justo Sierra" de l'UNAM, en avril-mai 1986. Au cours de cette mission, de variations hydrographiques d'amplitude moyenne comme les phenomenes cycloniques et anticycloniques, ainsi que l'upwelling, ont ete detectees dans la region. Les especes les plus abondantes etaient Stylocheiron carinatum (29,86%) suivie de Euphausia tenera (19,97%) et S. suhmi (15,18%). La richesse specifique augmentait dans les echantillons nocturnes; les densites etaient 3,07 fois plus elevees la nuit. Apparemment le comportement migratoire des Euphausiaces compensait l'effet attendu des particularites hydrographiques dans la communaute locale d'Euphausiaces. L'indice de Bray-Curtis a revele trois groupes de stations. Le premier representait l'influence des eaux cotieres et de la plate-forme continentale sur la communaute des Euphausiaces. Le second groupe etait une communaute mixte oceanique-plate-forme et le troisieme se rapportait aux eaux oceaniques oligotrophes du Golfe. Un quatrieme groupe incluait les zones peu profondes sans Euphausiaces. Les phenomenes anticycloniques relativement faibles n'avaient pas d'influence sur la communaute locale des Euphausiaces, bien que l'on se soit attendu a des densites d'Euphausiaces basses. Les phenomenes relativement plus marques, les cyclones, ont montre des densites moyennes plus elevees. Les densites d'Euphausiaces liees a l'influence des zones d'upwelling ont indique des valeurs similaires a celles relevees pour les anticyclones. Deux especes (S. suhmi and S. carinatum) sont presentes dans tout le Golfe du Mexique independamment des environnements consideres et du moment de la journee.

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