Phylogenetic and ontogenetic influences on the distribution of anthocyanins and betacyanins in leaves of tropical plants

We examined the anatomy of expanding, mature, and senescing leaves of tropical plants for the presence of red pigments: anthocyanins and betacyanins. We studied 463 species in total, 370 genera, belonging to 94 families. This included 21 species from five families in the Caryophyllales, where betacyanins are the basis for red color. We also included 14 species of ferns and gymnosperms in seven families and 29 species with undersurface coloration at maturity. We analyzed 399 angiosperm species (74 families) for factors (especially developmental and evolutionary) influencing anthocyanin production during expansion and senescence. During expansion, 44.9% produced anthocyanins and only 13.5% during senescence. At both stages, relatively few patterns of tissue distributions developed, primarily in the mesophyll, and very few taxa produced anthocyanins in dermal and ground tissue simultaneously. Of the 35 species producing anthocyanins both in development and senescence, most had similar cellular distributions. Anthocyanin distributions were identical in different developing leaves of three heteroblastic taxa. Phylogeny has influenced the distribution of anthocyanins in the epidermis and mesophyll of expanding leaves and the palisade parenchyma during senescence, although these influences are not strong. Betacyanins appear to have similar distributions in leaves of taxa within the Caryophyllales and, perhaps, similar functions. The presence of anthocyanins in the mesophyll of so many species is inconsistent with the hypothesis of protection against UV damage or fungal pathogens, and the differing tissue distributions indicate that the pigments may function in different ways, as in photoprotection and freeradical scavenging.

Ontogenetic Scaling of Poison Glands in Dendrobates Pumilio

The relationship between granular (poison) gland size and density was examined in an ontogenetic series of the strawberry dart-poison frog, Dendrobates pumilio. Specimens used in this study were collected from the La Selva Biological Station in northeastern Costa Rica. Patches of skin from the dorsal surface of seven frogs, ranging in size from 11 to 23 mm snout-vent length (SVL), were fixed and embedded in paraffin for histological sectioning. Poison gland size and density were quantified microscopically in these sections. Poison glands are uniformly distributed across the skin and mean poison gland diameter increases at a rate faster than snout-vent length from 42.5 at SVL 11mm to 120.0 at SVL 23 mm. Conversely, gland density decreases with body size from 71.9 glands/mm2 to 33.2 glands/mm2 • Due to the positive allometric growth of the poison glands, the percentage of skin surface occupied by poison glands increases from 10.1-22.1% in small frogs (SVL<18 >mm) to 50.0-65.2% in large frogs (SVL>19MM), resulting in more toxin per mm2 in the larger animals. The largest increase in toxicity is correlated temporally with the onset of sexual maturity rather than with changes in aposematic coloring.