Abstract Detail

Ecological Section

Mulroy , Thomas Wilkinson [1], Mulroy, Juliana C. [2].

Localized, Site-specific Shifts in Flowering Time Lead to Reproductive Isolation of Two Sympatric, Interfertile Forms of Dudleya brittonii (Crassulaceae) in Northern Baja California, Mexico.

We investigated patterns of flowering phenology in two easily-distinguished interfertile forms of a perennial succulent rosette plant in northwestern Baja California, Mexico. The silvery glaucous form is restricted to a bluff-forming volcanic formation along an approximately 13-mile (21-km) stretch of coastline. Within this range, the more widespread green form grows either (1) intermingled with the glaucous form on steep slopes (talus and soil) below outcrops occupied exclusively by the glaucous form or (2) separate from the glaucous form on nearby terraces and slopes. The green form extends both to the north and south of the area of overlap with the glaucous form.  This distributional pattern provides an unusual opportunity to separate physical from biotic factors in examining causes of observed flowering time differences. We estimated flowering initiation and termination dates from population samples of both forms. We quantified flowering periods of green populations at 16 locations, including locations in the area of overlap (green form growing either intermingled with or separate from the glaucous form) as well as locations to the north and to the south of the area of overlap. We also transplanted young individuals from different locations into a common garden and observed flowering times when they matured. At locations with intermingled green and glaucous plants, the mean dates of initiation and termination of flowering by green plants were delayed by a minimum of six weeks compared to locations where green plants grew separately from glaucous plants. Where the two forms grow intermingled, the mean initiation of flowering by green plants is generally after the mean termination of flowering by the intermingled glaucous plants, despite some overlap of late flowering glaucous individuals with early flowering green individuals. These location to location differences in flowering time are maintained when young plants transplanted to a common environment mature and flower. Thus it appears that that presence or absence of a close interfertile relative can force a temporal shift in flowering within a plant population, creating pre-zygotic reproductive barriers where the two come into contact and providing an example of reproductive character displacement. The differentiation of flowering times at such a local level is remarkable given the well-known propensity of Dudleya species to hybridize and is likely to be a factor in the relative infrequency of hybrids observed at these locations.  Because of the near reproductive isolation where they co-occur, we believe that these forms should be recognized as separate species.

1 - Leidos, Inc., Environmental Planning, 5464 Carpinteria Avenue, Suite K, Carpinteria , CA, 93013, USA
2 - Denison University, Department of Biology, Granville, OH, 43023, USA

Keywords:
character displacement
Flowering time
Dudleya
pre-zygotic barrier
hybridization 
sympatric speciation
parapatric speciation
Speciation
glaucous
flowering phenology
flowering period
sympatry
parapatry
Baja California
Crassulaceae
Coastal
Lithophyte
Fog
desert transition.

Presentation Type: Oral Paper:Papers for Sections
Session: 1
Location: Firs South/Boise Centre
Date: Monday, July 28th, 2014
Time: 9:30 AM
Number: 1007
Abstract ID:759
Candidate for Awards:None