Floral Nectar Secretion and Ploidy in Brassica rapa and B. napus (Brassicaceae). II. Quantified Variability of Nectary Structure and Function in Rapid-cycling Lines

Haploid, diploid and tetraploid lines ofBrassica rapaL. (syn.campestris),and allotetraploidB. napusL., were examined to determine theinfluence of ploidy on floral features, particularly nectarymorphology and anatomy, and to relate nectary structure to nectarproduction capacity. Except for haploids, all lines were rapid-cycling.Average flower dry weight, and petal length and width, werein the descending orderB. napus>B. rapa (4n) >2n>n.Pollen grains of 4nplants were larger than those of 2nplants;haploids lacked pollen. All lines developed nectaries. Typically, each flower producedtwo pairs of nectaries, of different types and nectar productioncapacity. Normally, each lateral gland was located above thebase of a short stamen, and together this pair yielded mostof a flower 's nectar carbohydrate. Each median nectary aroseat the outer junction of the bases of two adjacent long stamens.All lateral nectaries received a vascular supply of phloem alone,but median glands received reduced amounts of phloem, or lackedvasculature altogether. Most nectaries were solitary, but 14%of all flowers, and especially those of 2n B. rapa,had at leastone median and lateral gland connected. Obvious variation existed in nectary morphology between ploidylevels, between flowers of the same plant, and even within flowers.Ten forms of each nectary type were recognized. Plants producingthe most nectar carbohydrate had high frequencies of lateralnectaries which were symmetrical, unfurrowed swellings. TetraploidsofB. rapahad both the highest frequencies of furrowed lateralglands, and of isolated segments of nectarial tissue at thatposition. Even these separated nectarial outgrowths receivedphloem and produced a nectar droplet. At the median location,nectaries were commonly of two forms: peg- or fan-shaped. Lobeson median nectaries, up to four per nectary, were detected inalmost half of glands of 4nflowers examined; lobes were absentin haploids. Brassica rapa; Brassica napus; flower size; nectar production; nectary variability; petal size; ploidyphloem; pollen; rapeseed     

Infraspecific mitochondrial sequence diversity in Hydrobia ulvae and Hydrobia ventrosa (Hydrobiidae: Rissooidea: Gastropoda): Do their different life histories affect biogeographic patterns and gene flow?

Infraspecific relationships and population parameters are largely unknown in the ecologically significant mud snail genus Hydrobia s.I. We therefore studied infraspecific variation, population structure and gene flow in two Hydrobia species with different life history strategies: the marine, planktonic H. ulvae and the brackish-water, directly developing H. ventrosa. Based on sequencing data of a 638 bp fragment of the mtDNA gene for cytochrome oxidase 1, we found considerable differences between the two species. H. ulvae shows high average pairwisc nucleotide diversity, low population level differentiation (F_st). AND high average gene flow (Nm) between populations. Dispersal appears to accord with Wright's island model. In contrast, many populations of H. ventrosa have high population level differentiation and low gene flow. The average pairwise nucleotide diversity is relatively low; this species disperses according to Wright's isolation by distance model. Differences in dispersal modes and gene flow could be partly due to differences in type of early ontogeny and quantitative differences in passive dispersal. However, the fact that H. ulvae is a marine species with high tolerance to environmental stress and therefore less sensitive to migration barriers than H. ventrosa may better explain these differences. The extant lineages of H. ulvae and H. ventrosa most likely evolved in the northeastern Atlantic during the Pleistocene.