Life history traits in selfing versus outcrossing annuals: exploring the 'time-limitation' hypothesis for the fitness benefit of self-pollination

BACKGROUND: Most self-pollinating plants are annuals. According to the 'time-limitation' hypothesis, this association between selfing and the annual life cycle has evolved as a consequence of strong r-selection, involving severe time-limitation for completing the life cycle. Under this model, selection from frequent density-independent mortality in ephemeral habitats minimizes time to flower maturation, with selfing as a trade-off, and / or selection minimizes the time between flower maturation and ovule fertilization, in which case selfing has a direct fitness benefit. Predictions arising from this hypothesis were evaluated using phylogenetically-independent contrasts of several life history traits in predominantly selfing versus outcrossing annuals from a data base of 118 species distributed across 14 families. Data for life history traits specifically related to maturation and pollination times were obtained by monitoring the start and completion of different stages of reproductive development in a greenhouse study of selfing and outcrossing annuals from an unbiased sample of 25 species involving five pair-wise family comparisons and four pair-wise genus comparisons. RESULTS: Selfing annuals in general had significantly shorter plant heights, smaller flowers, shorter bud development times, shorter flower longevity and smaller seed sizes compared with their outcrossing annual relatives. Age at first flower did not differ significantly between selfing and outcrossing annuals. CONCLUSIONS: This is the first multi-species study to report these general life-history differences between selfers and outcrossers among annuals exclusively. The results are all explained more parsimoniously by selection associated with time-limitation than by selection associated with pollinator/mate limitation. The shorter bud development time reported here for selfing annuals is predicted explicitly by the time-limitation hypothesis for the fitness benefit of selfing (and not by the alternative 'reproductive assurance' hypothesis associated with pollinator/mate limitation). Support for the time-limitation hypothesis is also evident from published surveys: whereas selfers and outcrossers are about equally represented among annual species as a whole, selfers occur in much higher frequencies among the annual species found in two of the most severely time-limited habitats where flowering plants grow – deserts and cultivated habitats

Taller plants have lower rates of molecular evolution

Rates of molecular evolution have a central role in our understanding of many aspects of species' biology. However, the causes of variation in rates of molecular evolution remain poorly understood, particularly in plants. Here we show that height account

Functional distinctiveness of major plant lineages

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106060/1/jec12208.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/106060/2/jec12208-sup-0001-Supp_Info.pd

Meet Homo absurdus--the only creature that refuses to be what it is

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The sapiens advantage

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Reducing size to increase number: a hypothesis for compound leaves

Adaptive advantages of the compound leaf form in flowering plants have so far remained elusive.  A novel idea—proposed here—is that there are no direct advantages; the compound leaf evolved instead as a trade-off of selection in favour of something else: greater leafing intensity.  Producing more leaves per unit of supporting shoot or plant body size generates a larger ‘bud bank’— an aggregate of axillary meristems available for optimal deployment in strategies for growth, survival, and reproduction, and also facilitating capacity (through DNA replication errors) for generating novel adaptive mutations that can be transmitted through the germ line.  But higher leafing intensity requires that individual leaf mass be smaller.  Transition from a simple leaf (the ancestral form in angiosperms) to a compound leaf, therefore, may represent one mechanism whereby individual leaf mass was reduced within some angiosperm lineages.  Compound leaves however are rare in angiosperms, I suggest, because more parsimonious mechanisms for mass reduction in a simple leaf are likely to involve straightforward reductions in overall dimensions (length, width), or increased lobing