Some patches and even entire populations lose males or, more rarely, females. 2002). (2005b)]. Copyright © 2006 Elsevier B.V. All rights reserved.

5b). These half-stars then grow three new arms. The biology of asexual reproduction in the fissiparous brittle star Ophiocomella ophiactoides (H.L. (i) For unrestricted recruitment, the male proportion ranged from 0.36 to 0.12 with increasing dispersal distance.

Morgado, E.H. and Tonaka, M.O. By November, most sex structures are gone. An upper limit on the rate of sporeling establishment (i.e. The impact of asexual and sexual reproduction in spatial genetic structure within and between populations of the dioecious plant Marchantia inflexa (Marchantiaceae).

A random‐generated number was compared with pd′ for applying disturbance to the patch. M. inflexa is an ideal species for addressing this issue because (i) each individual is only one of the two sexes (sex is chromosomally determined); (ii) some single‐sex populations of this dioecious species are known to exist (Schuster 1992), indicating that complete loss of a sex is at least possible; (iii) considerable empirical information is available on sex‐specific clonal expansion by growth and asexual reproduction, both from field and from glasshouse studies (McLetchie & Puterbaugh 2000); and (iv) models of sex‐specific dynamics within individual patches have already been developed and parameterized for this species (McLetchie et al. We then present our results, emphasizing the relationship between single‐patch and patch‐assemblage dynamics and including a thorough analysis of the key features.

As we mentioned previously, Maynard Smith (1978) pointed out that, because sexual and asexual propagules in species that produce both are often adapted to different ecological situations, the mixed mode of reproduction could readily be maintained by environmental heterogeneity. This suggests that some patches may act as sources and others simply as sinks for dispersing spores. Next we describe our metapopulation model – an array of patches, each linked to the others by spore dispersal, subjected to extinction and following single‐patch dynamics as in McLetchie et al.

The extent of patch coverage or occupancy by these units and the corresponding stages are simulated dynamically. A small number of five- and seven-armed individuals resulted from natural variability in fission and regeneration processes.

At stages 3 and 6, the icons show thalli with cups that produce gemmae (asexual propagules; centre picture).

Chao, S.M., Tsai, C.C.

The basic features of ecological sex ratio dynamics that favour coexistence of the sexes at the metapopulation level are those that permit sexual recruitment sufficient to ameliorate the dominant biasing mechanism favouring one sex over the other. Male proportions above 0.2 were found for both the lowest and the highest establishment rates.

Stage 7 females can be fertilized at a rate proportional to the abundance of stage 4 males, thereby shifting females from stage 7 to stage 1 at fertilization. These studies suggest that metapopulation dynamics are limited for explaining gynodioecy. New substrate is made available by disturbances (especially flooding) within patches and by whole‐patch elimination. This estimation, derived from a single sampling effort, was higher than the temporal averaged metapopulation male proportion (0.128), while the spatial standard deviation for both theoretical and field data shared similar large variation (±0.20). 4.2.

Mode of production of broods Like all brittle stars, they also reproduce sexually. Each of these gemmae (~0.12 mm in diameter) can produce a new individual genetically identical to the parent plant.

Other parameters are at default values. We tested this in the sea anemone Actinia tenebrosa by comparing cycles of reproductive activity and the mode of production of brooded larvae in local populations occupying boulder fields and stable rock platforms. In this system, gender has a complex inheritance often determined by epistatic interactions between nuclear and cytoplasmic genes.

1(a) taken to be linearly determined by the donor‐stage (Table 1). Ecological aspects of ophiuroids from the phytal of S.W. Population sex ratios, sex‐specific clonal traits and tradeoffs among these traits in the liverwort, Bryophyte dispersal inferred from colonization of an introduced substratum on Whiteface Mountain, New York, The Evolution of Asexual Reproduction in Plants, Spatial patterns of seed dispersal, their determinants and consequences for recruitment, The evolutionary significance of asexual reproduction in mosses, The maintenance of gynodioecy and androdioecy in a metapopulation, A hypothesis for the evolution of androdioecy: the joint influence of reproductive assurance and local mate competition in a metapopulation, Evolution of aquatic angiosperm reproductive systems, Sexual dimorphism in biomass allocation and clonal growth of, Life‐cycle graphs and matrix modeling of bryophyte populations, VI. 2(b). P:181.

McGovern, T.M. M7 represents a fertilization rate.

2002). 566:1-567. Increased transition rates from non‐reproductive stages to sexual stages (T42 and T75) favoured males (Table 3). 1994. The female competitive advantage dominated the re‐establishment of males from spores except under weak constraints on spore establishment and uncovered threshold.

Therefore, a multipatch study of M. inflexa based on these previous investigations can determine whether metapopulation characteristics may help retain both sexes, and thus sexual reproduction in a patch assemblage, under conditions leading to loss of a sex in single patches. Marchantia inflexa is a thalloid dioecious liverwort that ranges from northern Venezuela to the south‐eastern USA (Bischler 1984). The metapopulation dynamic model of M. inflexa extends the analysis of McLetchie et al.

1a). Even high distances of gemma dispersal were unable to create much of a gender bias, as males have only a modest advantage in gemma production on a per‐unit basis.

Local and metapopulation sex ratios were the focal response variables. Most O. ophiactoides were in various stages of recovery following fission, having three long and three shorter arms. 1b).

was studied during June, July, August and December, 1981 and July, 1982. One relevant aspect in species capable of both types of reproductions is the ecological specialization of the propagules. Moreover, our modelling results were particularly sensitive to our glasshouse data and how they might translate into field growth rates (Fig.

Learn more. The metapopulation favoured the coexistence of sexes by initiating patches at 1 : 1 sex ratio and by intervals of reduced growth competition in which the male advantage in production of asexual propagules predominates.

We determined seasonal patterns of brooding and gonad development by monthly dissection of 15–30 adults from each of two boulder fields and two stable platforms. Of particular importance is the quantitative documentation of field sex ratio and the loss of one or both sexes at the patch and metapopulation level, propagule dispersal within and between patches, and patch extinction and recolonization rates. Although few studies have looked for intraspecific variation in reproductive tactics, flexible expression of such life-history traits may be favoured in species that occupy a range of habitats. 2005b), and to consider the implications of variation in distances and patch sizes within the metapopulation (C.R.

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