HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Decker, K. L. Articles by Pilson, D. Search for Related Content PubMed PubMed Citation Articles by Decker, K. L. Articles by Pilson, D. Agricola Articles by Decker, K. L. Articles by Pilson, D.

Biased sex ratios in the dioecious annual Croton texensis (Euphorbiaceae) are not due to environmental sex determination¹

¹ School of Biological Sciences, 348 Manter Hall, University of Nebraska, Lincoln, Nebraska 68588-0118 USA

ABSTRACT

At Arapaho Prairie, in the sandhills of western Nebraska, the dioecious annual Croton texensis (Euphorbiaceae) exhibits biased sex ratios. Moreover, the direction of bias changes from year to year: in 1994 the study population was significantly female biased, in 1995 and 1996 it was significantly male biased, and in 1997 and 1998 the sex ratio did not differ from 1 : 1. Such variation in the observed sex ratio in plants is frequently attributed to environmental sex determination (ESD), which is favored by natural selection if the rate of fitness gain across an environmental gradient is greater for one sex than the other. We performed experiments to determine: (1) whether variation in the sex ratio is correlated with environmental conditions, as would be expected if ESD is operating, and (2) whether ESD, if present, would be favored by natural selection. In a common garden experiment in which water and fertilizer were manipulated the sex ratio was marginally male biased in treatments in which water was added, but not different from 1 : 1 in other treatments. In field plots into which seeds were planted none of several soil characteristics, nor overall plot quality for C. texensis (measured as average plant biomass) were correlated with plot sex ratio. However, plots in which a large number of planted seeds emerged tended to be female biased. These results provide very weak evidence for sex ratio bias across an environmental gradient, and thus provide little evidence for ESD. Moreover, sex-by-environment interactions for fitness, which are required for the evolution of ESD, were absent for all measured variables. Thus, ESD does not appear to be favored by natural selection in this population. Instead, these biases may have been caused by differences between the sexes in germination and/or early mortality.

Key Words: Croton texensis • environmental sex determination • ESD • Euphorbiaceae • sex ratio

This article has been cited by other articles:

				P. E. Berry, A. L. Hipp, K. J. Wurdack, B. Van Ee, and R. Riina Molecular phylogenetics of the giant genus Croton and tribe Crotoneae (Euphorbiaceae sensu stricto) using ITS and TRNL-TRNF DNA sequence data Am. J. Botany, September 1, 2005; 92(9): 1520 - 1534. [Abstract] [Full Text] [PDF]