Abstract Detail

Conservation Biology

NegronOrtiz, Vivian [1].

Sex expression and reproduction of federally threatened Euphorbia telephioides (Euphorbiaceae), a North-American endemic species.

To understand the conservation requirements for the recovery of Euphorbia telephioides Chapman (telephus spurge), I am investigating reproductive biology and in-situ seed germination. Three 10 m² plot were established in each of the three counties of north-west Florida where this species occurs, and size and reproductive parameters were recorded for four years. Each population had more reproductive than sterile plants in each of the four years. Among reproductive plants, three sexual morphs were distinguished on examination of the cyathia: plants with male cyathia, plants with female cyathia, and plants with variable sex expression. These variable individuals had both male and female unisexual cyathia, or both perfect and unisexual cyathia, on the same plant (monoecious, mn). Therefore, this species is polygamous. Morph frequencies did not differ annually (F=0.09, p=0.76), however, sex expression was significantly female-biased (F=71.9, p<0.0001). A small proportion of male plants that shifted to monoecy were associated with a fire event suggesting responsiveness of sex expression to environmental factors; sex switching was not observed on plants that were not subjected to fire. The length of the longest stem and stem diameter imply a threshold size for reproduction. The stem was significantly larger on reproductive plants than sterile (mean= 12.6 vs. 8.3 cm, F = 403.3, p < 0.0001). Females had significantly longer stems than the other morphs (mean f = 13.2, m = 11.2, mn = 9.3 cm; F = 19.29, p < 0.0001), but stem diameter was significantly greater for monoecious plants (F = 21.38, p < 0.0001). In contrast, females had shorter inflorescences (F = 69.95, p < 0.0001) and fewer flowers (F = 72.3, p < 0.0001), but on average, produce more fruits than monoecious plants. Flowers that mature at different times during the flowering season produce seeds that vary in the ability to germinate. Seeds collected during late August or early September germinated the next spring. Of 292 seeds collected, 71 % were viable. In-situ seed germination and seedling survival was low with only 14 % germinating during the first year and 7 % surviving the second year. Results suggest a lack of seed bank since non-germinated seeds were not persistent in the soil. These results suggest size-dependent variation in gender appears to be part of an adaptive life history of E. telephioides and that conservation efforts must consider studies on fire dependence for the recovery of this taxon.

1 - U.S. Fish And Wildlfe Service, 1601 Balboa Avenue, Panama City, FL, 32405, USA

Keywords:
Sex expression
Euphorbia telephioides
reproductive biology
in-situ seed germination
federally listed
Florida
Conservation.

Presentation Type: Oral Paper:Papers for Topics
Session: 27
Location: Firs North/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 2:15 PM
Number: 27004
Abstract ID:353
Candidate for Awards:None