Damage and shade enhance climbing and promote associational resistance in a climbing plant

1. Associational resistance occurs when one plant species gains protection from its consumers by association with a defended species. In semi-arid ecosystems of Chile, the perennial herb Convolvulus chilensis (Convolvulaceae) suffers heavy herbivory by small mammals when growing prostrate but plants seem to be protected when they are climbing onto cacti or thorny shrubs (nurse species). 2. Field observations suggest that damaged main stems have a greater number of small lateral stems, which greatly enhance climbing success. In this field study we addressed whether C. chilensis shows associational resistance by climbing onto nurse species, and evaluated whether damage and also shade (a cue for neighbour presence) elicit architectural responses that enhance climbing probability. 3. We documented associational resistance for C chilensis: climbing individuals growing associated with cacti and thorny shrubs suffered less herbivory (percentage of damaged stems: 35 vs. 98) and had greater reproductive output (number of reproductive structures at the end of the season: 150 vs. 0) than prostrate individuals growing in isolation. Experimental clipping of the main stem caused plants to produce a greater number of lateral stems both in sun (70% increase) and in shade (66% increase) treatments. Moreover, stem damage caused a 50% increase in the number of stems actually climbing on a support, but only in shade. 4. Synthesis. We show for the first time that phenotypic responses to herbivory of the potentially protected species may enhance association with the defended nurse species, thereby promoting associational resistance. This finding adds a new perspective for mechanistic studies of positive interactions among plants, suggesting that behavioural responses of the protégée may mediate the magnitude of nurse effects

Morfologia polínica de espécies do gênero Merremia Dennst. (Convolvulaceae) ocorrentes no Estado da Bahia, Brasil Morphology pollen of species genus Merremia Dennst. (Convolvulaceae) ocurring in Bahia State, Brazil

O gênero Merremia (Convolvulaceae) teve as espécies nativas na Bahia inventariadas e estudadas sob o ponto de vista palinológico. Foram registrados nove táxons do gênero: M. aegyptia (L.) Urb., M. cissoides (Lam.) Hallier f., M. digitata (Spreng.) Hall. f. var. digitata, M. digitata var. ericoides (Meissn.) Austin & Staples, M. dissecta (Jacq.) Hall. f. var. edentata (Meisn.) O'Donell, M. flagellaris (Choisy) O'Donell, M. macrocalyx (Ruiz et Pav.) O'Donell, M. tomentosa (Choisy) Hall. f. e M. umbellata (L.) Hall. f. Em M. digitata var. digitata e M. flagellaris os grãos de pólen apresentavam-se irregularmente e com três e seis colpos; membrana apertural espessa em M. aegyptia, M. cissoides, M. digitata var. ericoides; a exina é espessa e granulada em todas as espécies, o teto é fino; sexina mais espessa que nexina. Os grãos de pólen com 6 aberturas são zonocolpados (M. umbellata) ou pantocolpados (M. digitata var. digitata, M. digitata var. ericoides, e M. flagellaris), podendo ocorrer em um mesmo espécime mais de um tipo apertural de grão de pólen. Os dados palinológicos observados vêm fortalecer a união das espécies M. aegyptia, M. dissecta var. edentata e M. macrocalyx em M. sect. Schizips, M. umbellata em M. sect. Xanthips e as demais em M. sect. Cissoides. Nesta última seção, com exceção de M. tomentosa, as espécies restantes pertencem ao complexo M. digitata. No referido complexo as espécies não estão bem delimitadas sendo necessário que estudos mais profundos sejam realizados afim de melhor delimitá-las.<br>Species of the genus Merremia (Convolvulaceae) from State of Bahia were surveyed, and their pollen grains were studied by usual methods. Nine taxa were recorded: M. aegyptia (L.) Urb., M. cissoides (Lam.) Hallier f., M. digitata (Spreng.) Hall. f. var. digitata, M. digitata var. ericoides (Meissn.) Austin & Staples, M. dissecta (Jacq.) Hall. f. var. edentata (Meisn.) O'Donell, M. flagellaris (Choisy) O'Donell, M. macrocalyx (Ruiz et Pav.) O'Donell, M. tomentosa (Choisy) Hall. f. and M. umbellata (L.) Hall. f. In M. digitata var. digitata and M. flagellaris, the pollen grains presented irregular colpi and with three and six long colpi. Thick apertural membrane was observed in M. aegyptia, M. cissoides, M. digitata var. ericoides; presence with opercules in M. aegyptia, M. cissoides and M. digitata var. ericoides pollen grains. Six-aperturated pollen grains are zonocolpate (in M. umbellata) or pantocolpate (in M. digitata var. digitata, M. digitata var. ericoides and M. flagellaris); more than one apertural type can be found grains in the same specimen. The palinological data corroborate the placement of M. aegyptia, M. dissecta var. edentata and M. macrocalyx in M. sect. Schizips, M. umbellata in M. sect. Xanthips and other ones in M. sect. Cissoides. In the latter section, excluding M. tomentosa, all species belong to the complex M. digitata, in which they are not well delimitated