Compensatory reproduction in a biennial herb following insect defloration

Abstract

The ability of the biennial herb, Pastinaca sativa L. (wild parsnip), to respond to and compensate for destruction of primary umbel seeds by the larvae of Depressaria pastinacella (Lepidoptera: Oecophoridae) was analyzed by comparing umbel and seed production of damaged and undamaged plants collected from five populations. Plants with a basal stem diameter smaller than 8 mm suffer a reduction in seed set of about 50% when the primary umbel is destroyed but larger plants are able to compensate for loss of primary umbel seeds by increased seed set of tertiary umbels. Depending on plant size, this is due to either an increase in the number of tertiary umbels that reach maturity or an increase in the number of seeds per tertiary umbel. Although seeds of tertiary umbels are significantly smaller than those of primary or secondary umbels, their viability is equivalent to that of secondary seeds and may be greater than that of primary seeds. Characteristics of P. sativa's reproduction, such as the long flowering period and the initiation of more umbels than the plant is normally able to bring to maturity, are important to P. sativa's ability to compensate for the effects of herbivore damage.

Variation in Seed Weight and Its Effects on Germination in Pastinaca Sativa L. (Umbelliferae)

“…The study was initiated because in large individuals of P. sativa (basal stem diameter [BSD] of the flowering stalk > 12 mm) destruction of the primary (first) inflorescence by Depressaria pastinacella (Duponchel) (Lepidoptera: Oecophoridae) leads to increased seed set on tertiary inflorescences produced later in the growingseason (Hendrix,1979).Althoughtotalseed number does not diffier between damaged and undamaged plants, seeds from tertiary inflorescences generally weigh less than the seeds they replace (Hendrix, 1979). Therefore, an analysis of the eXects of herbivory on fitness in P. sativa must take into account potential diffierences in germination due to diffierences in seed weight.…”

Does pre-dispersal seed predation limit reproduction and population growth in the alpine clonal plant Geum reptans?

“…Seeds originating from an uninfested population served as control Clearly, developing reproductive structures are a sink continuously requiring the supply of resources (Lee 1988), and the removal of a fraction of this sink may lead to a change in resource allocation (Hendrix 1988). Removal of seeds has been observed to result in the production of additional flowers or fruits as an effect of reduced floral abortion (Hendrix 1979;Islam and Crawley 1983;Lehtilä and Syrjä nen 1995). Nevertheless, compensation in growth due to herbivory is controversially discussed (e.g.…”

“…Hendrix 1979;Louda 1982;Louda and Potvin 1995;Briese 2000;Leimu et al 2002) and altering flowering phenology (e.g. Janzen 1971;Eriksson 1995;Louda and Potvin 1995;Albrectsen 2000;Mahoro 2002;Russell and Louda 2004).…”

“…Compensation for seed losses might particularly evolve in plants subjected to a predictable risk of damage by host-specific herbivores (Crawley 1983;Jä remo et al 1996). As a consequence, resources that would have been used for seed and fruit maturation may be stored, may be allocated into compensatory flowers or fruits that would normally been aborted or may be used for the production of non-reproductive tissue (Janzen 1971;Hendrix 1979;Crawley 1997). Accordingly, for clonal plants it could be inferred that the loss of seeds due to predation may alter the balance between sexual reproduction and clonal growth in favour of the latter.…”

THE RESPONSES OF CYNOGLOSSUM OFFICINALE L. AND VERBASCUM THAPSUS L. TO DEFOLIATION IN RELATION TO NITROGEN SUPPLY *

“…Since both plant survival and seed output are strongly correlated to plant size in short-lived plants (van der Meijden & van der Waals-Kooi, 1979), growth rate and regeneration time eventually determine reproduction expressed in the number of seeds. In some short-lived plants, the final output of number of seeds increases after herbivory (Hendrix, 1979(Hendrix, , 1984 and there is evidence from some species that the growth rate of defoliated individuals is higher than that of undefoliated plants of the same size and life stage (Alcock, 1964).…”