Individual variation in pathogen attack and differential reproductive success in the annual legume,Amphicarpaea bracteata

Summary Demographic analyses in two natural populations of the annual legume Amphicarpaea bracteate examined whether variation in attack by the host-specific fungal pathogen Synchytrium decipiens was associated with variation in the reproductive success of individual plants. In both populations, fungal infection early in life was significantly associated with reduced seedling growth rates. Laboratory inoculation experiments confirmed that S. decipiens infection had a negative impact on plant growth. The laboratory experiments further indicated that there was significant variation among the progenies of different plant genotypes in the degree of growth reduction caused by pathogen attack. Prereproductive mortality rates in natural environments were significantly higher for plants with infection intensities above the median; for the two populations studied, heavily infected plants had 3.8 and 12 gimes higher death rates compared with low infection plants. Among surviving plants, fungal infection intensity was significantly negatively correlated with total seed biomass in both populations. As a result of these associations between plant survivorship, fecundity, and fungal infection, lifetime relative fitness within both plant populations was strongly negatively correlated with the intensity of S. decipiens infection. These results demonstrate the existence of consistent natural selection for increased resistance to pathogen attack in this plant species.     

Floral biology, reproductive system and reproductive success of Macroptilium fraternum (Fabaceae)

Observations about the floral biology and the reproductive system of Macroptilium fraternum were made in two populations in Argentina, with different edaphic conditions, situated at the southern area of distribution of the species. The coexistence of two kind of flowers in the same plant was detected in both populations and in herbarium material from other localities: a) cleistogamous preanthesis flowers and b) pseudocleistogamous flowers. The cleistogamous preanthesis flowers possessed wings longer than 5 mm and were disposed in pubescent, erect, racemes exposed above the level of the foliage. The anthesis lasted approximately 5 hours on sunny days or 9 hours on rainy days, the right wing covered the left wing, the corolla acquired a bilabiate aspect, offering the left wing as landing platform; they produced a low quantity of nectar (0.18 +/- 0.13 microliter); they did not receive pollinator visits; approximately four hours after the beginning of the anthesis on sunny days the ovary started to grow; in the bud, the receptive stigma was covered with germinating pollen grains from the same floral unit. The pseudocleistogamous flowers possessed wings shorter than 5 mm that were disposed in brief, hirsute and prostrate racemes, non subterranean as in other Macroptilium species; the banner started to spread exposing partially the wings, the left wing limb surrounded the keel and never spread; the right wing started to spread and after 2 seconds refolded and began to wither, the ovary began to grow immediately; the flower did not offer a surface to allow visitors to settle; in the buds the stigma was receptive and found with pollen grains from the same floral unit emitting their tubes. The relative reproductive success was low (natural pollination = 8%; spontaneous self-pollination = 3%), probably due to the low pollen viability, the high percentage of seed abortion and the lack of pollinator's visits. The production of both flower types is not conditioned by edaphic factors, as they were found in plants belonging to different environments. Study of the progeny of both floral types in both populations has demonstrated that each one produces a similar amount of seeds contributing to the next generation with plants of similar characteristics (slow development, low resistance to infections and high mortality). The absence of pollinators in these flowers (in part because they preferred to visit flowers of other species with more reward and in part because of the fragmentation of the habitats), would be producing inbreeding depression in the studied populations; if the germplasm variability is not preserved, these populations situated at the Southern end of the distribution range of the species could become extinguished.     

Plant size,breeding system,and limits to reproductive success in two sister species of Ferocactus (Cactaceae)

Plant reproductive output can be limited by a variety of factors, bothintrinsic and extrinsic. I investigated the reproductive biologies of twospecies of unbranched short-columnar cacti, Ferocactuscylindraceus and F. wislizeni. I recordedfemalereproductive output (flowers produced, fruit set, seeds per fruit and seedmass), plant size and growth, and used hand-pollination experiments todeterminebreeding systems and pollen limitation. In both species, the ability to selfvaried among individuals, but self-pollination resulted in very few seeds,suggesting strong inbreeding depression. Neither species was pollen-limited.Numbers of flowers produced increases with plant size for both species, andseeds per fruit may also be related to plant size, although the relationship isunclear. Seed mass is not correlated with plant size. Flower production wassimilar in both species, but F. cylindraceus producedfewerseeds per fruit than F. wislizeni, and its seeds weighedless. Fruit set by F. cylindraceus was heavily impacted bya florivorous lepidopteran. Fruit set was very high (94 to 96%) inF. wislizeni, suggesting that architectural constraints(e.g., meristem limitation) are more limiting than resource levels or the levelof pollinator services. In F. cylindraceus, numbers ofseeds per fruit was positively correlated with seed mass, whereas inF. wislizeni, the relationship was negative (tradeoff).Thegrowth rates of F. wislizeni are affected by rainfall theprevious season, and growth rates increase as the plant ages.Ferocactus cylindraceus and F.wislizeni are thought to be sister species, meaning that observeddifferences between them are more likely to be the result of recentevolutionaryprocesses in their lineages rather than differing phylogenetic histories.     

Isozyme variation and the reproductive biology of Hydrocharis morsus-ranae L. (Hydrocharitaceae)

Electro-phoretically detectable isozyme variation was studied for 17 enzyme systems in several N American populations of the introduced aquatic plant Hydrocharis morsus-ranae and in two European populations. Twenty-nine loci were inferred from progeny, adult and turion enzyme banding patterns with 28 of these loci homozygous in all individuals studied. Malate dehydrogenase-1 (MDH-1) was the only locus which could be interpreted as multi-allelic and heterozygous. Twenty-seven of 76 seedlings assayed showed an age specific expression for an alcohol dehydrogenase locus (ADH-2) never seen in adults or turions. Since all adults sampled were phenotypically identical at all loci assayed, it is possible that only one isozyme genotype of this species is present in N America. European turion data further indicated that the populations studied were identical to N American plants sampled at all loci except EST. Therefore, although H. morsus-ranae is dioecious, outcrossing appears to involve substantial inbreeding. Connections between extensive inbreeding and the failure of effective sexual reproduction are considered.     

Factors influencing reproductive success in the clonal moss, Hylocomium splendens

Female reproductive success in the unisexual perennial clonal moss Hylocomium splendens was examined by recording, if the segment was reproductive [produced sporophyte(s)] or not, together with several distance-to-male and male density variables, and segment size. This was done for every female segment in a population over a 5 year study period. A high fraction of the population could be sexed because we monitored the population in situ for 5 years, and thereafter harvested the population for electrophoretic analysis from which the clonal identity and expressed sex could be deduced. Fertilization distances in H. splendens were short, indicated by the fact that as many as 85% of the female segments with sporophytes were situated within a distance of 5.0 cm from the nearest male. The longest distance measured between a sporophytic female and the closest male was 11.6 cm. However, analysed within a generalized linear modelling (GLM) framework, the year was the best single predictor for the presence of H. splendens sporophyte although female-segment size and distance to the closest situated male were also strongly significant. The two latter factors explained larger fractions of variation in sporophyte presence in a GLM model with three predictors than in single-predictor models. This is because (i) the large variation in sporophyte production among years partly obscures the strong general increase in sporophyte production with increasing female-segment size and vitality, and (ii) the between-year variation and the size obscure the effect of the distance to the most proximate male. To our knowledge, this study is the first to incorporate into one model the relative importance of several factors for bryophyte reproductive success. Our results demonstrate the value of multiple-predictor approaches in studies of reproductive success.     

Diversity of seed storage protein patterns in wild peanut (Arachis,Fabaceae) species

55 accessions of wild peanuts (Arachis spp.) introduced from South America were analyzed for seed storage protein composition using SDS-PAGE electrophoresis. The objectives of the study were to evaluate variability within sect.Arachis and to classify taxa based on protein composition. 25 different band positions were resolved. Individual accessions had 11 to 18 bands which included the conarachin region (MW > 50 kD), two to five bands in the acidic arachin region (MW 38–49.9 kD), three to seven in the intermediate MW region (23 to 37.9 kD), two to five bands in the basic arachin region (18–22.9 kD), and one to three bands in the low MW protein region (14–17.9 kD). These data were utilized in a principal coordinate analysis based on the matrix of genetic distances between all pairs of the 55 accessions. Several groups of accessions conformed to expected species classification includingA. batizocoi, A. stenosperma, andA. monticola; whileA. duranensis, A. cardenasii, A. helodes, andA. correntina did not form good groups. The study showed that great diversity exists for protein profiles and seed storage proteins have potential for aiding species classification and for serving as markers for interspecific hybridization studies.     

Electric signalling and reproductive behaviour in a mormyrid fish, the bulldog Marcusenius macrolepidotus (South African form)

Bulldog fish (Marcusenius macrolepidotus) generate short (<1 ms) electric-organ discharges (EODs), separated by much longer and highly variable interdischarge intervals (IDIs). We observed overt behaviour and electrical activity during reproductive behaviour in a male and in a female bulldog, and identified IDI patterns with putative signal functions. In contrast to Pollimyrus adspersus and Pollimyrus isidori, in which an elaborate and extended courtship precedes spawning proper, our fish started spawning almost immediately when we allowed the female to enter the males territory. The male did not construct a nest, and neither parent provided parental care. The male showed very little aggression towards the intruding female. Fish spawned in bouts near the males hiding place, and eggs were scattered by the females vigorous tail flips as she left the spawning site, only to return shortly thereafter. During spawning bouts, both fish generated highly stereotyped IDI patterns: the male generated a series of IDIs gradually decreasing from about 200 ms to about 55 ms that was abruptly terminated by a long IDI. The female generated a series of relatively regular IDIs (about 54 ms) that was followed by a marked increase in IDI duration (the probable time of spawning). Finally, a sharp decrease in IDIs to about 20 ms accompanied the females sudden escape from the spawning site. In between spawning bouts, both fish generated series of very short IDIs (high discharge rate, HD) that alternated abruptly with very low-rate inter-HD activity (especially in the male). IDIs as short as 9 ms (male) or 11 ms (female) occurred during HD displays. No visible aggression, in fact very little overt behaviour, occurred during these HD displays in both fish. Agonistic interactions between male and female, outside a reproductive context, were similar to those previously described in male pairs, including overt behavioural patterns such as parallel swimming, antiparallel display and attack, as well as HD displays. When not interacting, fish did not generate HD displays. We suggest the HD display is a communication signal in both reproductive and agonistic contexts.     

Growth rates and auxin effects in graviresponding gynophores of the peanut, Arachis hypogaea (Fabaceae)

The gynophore of the peanut plant (Arachis hypogaea) is a specialized organ that carries and buries the fertilized ovules into the soil in order for seed and fruit development to occur underground. The rates of growth of vertically and horizontally oriented gynophores were measured using a time-lapse video imaging system. We found that the region of maximum extension growth due to elongation (termed the Central Elongation Zone) is located on average at 2-5 mm from the tip. In the first 0-4 h after horizontal reorientation (gravistimulation), new zones of growth emerge on the upper surface, while the elongation zone of the lower side decreases in size and magnitude. Four to six hours after reorientation the zones of maximum growth are almost equal in size and location on the upper and lower sides. The growth rate and the gravitropic response decreased dramatically, upon the excision of the ovule region (terminal 1.5 mm), but a gravitropic growth response could be restored by applying the auxin indole-3-acetic acid exogenously to the excised tip. The addition of napthylphthalamic acid (an auxin transport inhibitor) at the ovule region allowed some growth to occur, but the gynophores do not respond normally to gravity, upon horizontal reorientation. We discuss the role of auxin in the gravitropic response of the gynophore.     

State of the reproductive system of populations of species of the genus Glycyrrhiza L. (Fabaceae)

Reproductive features of the valuable medicinal herbs Glycyrrhiza glabra L., G. uralensis Fisch., and G. korshinskyi Grig. were investigated; an assessment was made of the state of the reproductive systems of populations located under introduction conditions in the Central Urals and in the zone contact of the species ranges in the southern cis-Urals. The states of the male and female reproductive systems, seed productivity elements, pollination features, and the viability of seeds produced by different pollination treatments were studied. For the three Glycyrrhiza species, the seed productivity indices were found to decrease considerably starting from the early stages of development of the female reproductive system and continuing to seed maturity. A quantitative analysis of seed productivity elements taking into account the flowering duration of the species showed that the seed production system of the species is very efficient; even in the introduced populations located north of the range, it is able to produce viable seeds in years with favorable growing conditions. Qualitative and quantitative indices of the reproductive system were used to characterize samples from the zone of contact between the ranges. Embryological analysis confirmed the possibility of interspecific hybridization and the prevalence of hybrid forms among the samples. A broad distribution of interspecific hybridization in Glycyrrhiza in various parts of the ranges is assumed. Glycyrrhiza species are characterized by seed and vegetative reproduction. Vegetative reproduction is limited in space but efficiently ensures reproduction of individuals and formation of vegetative clones. Seed reproduction is characterized by indices such as amphimictic seed formation, strict entomophily, and interspecific compatibility. Seed reproduction is a factor that controls the possibility of wide propagation of the genetic material in space and, hence, the formation of mixed and hybrid populations leading to a higher intraspecific and interspecific diversity of the genus.     

Origins of resistances to rust and late leaf spot in peanut (Arachis hypogaea,Fabaceae)

The cultivated peanut (Arachis hypogaea, Fabaceae) is believed to have originated along the eastern slopes of the Andes in Bolivia and northern Argentina. The crop is now grown throughout tropical and warm temperate regions. Among diseases attacking peanuts, rust caused byPuccinia arachidis and late leaf spot caused byPhaeoisariopsis personata are the most important and destructive on a worldwide scale. Both pathogens, restricted in host range to Arachis, probably originated and coevolved in South America along with their hosts. In recent years there has been much emphasis on screening of peanut germplasm for resistance to these diseases. At the International Crops Research Institute for the Semi-Arid Tropics (ICRISA T), India, some 10,000 peanut germplasm accessions were screened for resistance to rust and late leaf spot during 1977–1985 and sources of resistance indentified for either or both pathogens. Of the resistant genotypes, about 87% belonged to A. hypogaea var.fastigiata and 13% to var.hypogaea; 84% originated in South America or had South American connections. A high percentage (75%) had their origin in Peru (believed to be a secondary gene center for var.hirsuta and var.fastigiata,), suggesting that resistance to rust and late leaf spot diseases might have evolved in that country.     

Inbreeding depression and mating-distance dependent offspring fitness in large and small populations of Lychnis flos-cuculi (Caryophyllaceae)

The spatial structure of four Lychnis flos-cuculi populations, varying in size and degree of isolation, was studied by comparing the fitness of offspring resulting from self-pollination and pollinations by neighbouring plants, plants within the same population, and plants from other populations. Selfed offspring had the lowest fitness of the four offspring groups. No significant difference was found between the performance of offspring from pollinations by neighbouring plants and offspring pollinated by plants further apart but within the same population. A lower fitness of offspring from pollinations between neighbours would be expected if these matings, on average, yielded inbred offspring which suffered from inbreeding depression. These results imply that either a tight neighbourhood structuring is not present, or that the inbreeding depression for offspring by neighbours is too low to detect, although these are inbred. Crossings between populations produced offspring with a significantly higher fitness than offspring sired within populations. There were no significant differences in response to inbreeding among the populations, and differences in mean fitness among populations had no clear relation to the population size or degree of isolation. A reduced fitness of small populations due to inbreeding depression or a less severe response to experimental inbreeding due to purging of deleterious alleles is therefore not supported by our results.     

Host mating system and the spread of a disease-resistant allele in a population

The model presented here modifies a susceptible-infected (SI) host–pathogen model to determine the influence of mating system on the outcome of a host–pathogen interaction. Both deterministic and stochastic (individual-based) versions of the model were used. This model considers the potential consequences of varying mating systems on the rate of spread of both the pathogen and resistance alleles within the population. We assumed that a single allele for disease resistance was sufficient to confer complete resistance in an individual, and that both homozygote and heterozygote resistant individuals had the same mean birth and death rates. When disease invaded a population with only an initial small fraction of resistant genes, inbreeding (selfing) tended to increase the probability that the disease would soon be eliminated from a small population rather than become endemic, while outcrossing greatly increased the probability that the population would become extinct due to the disease.     

Effects of self-pollination and maternal resources on reproduction and offspring performance in the wild lupine, Lupinus perennis (Fabaceae)

We examined the effects of self-pollination and resource addition to maternal plants of Wild Lupine on seed production in the field, and on offspring performance in the greenhouse. Although 24% of flowers set fruits when open-pollinated, only 11% of flowers set fruits when self-pollinated. Self-pollination significantly reduced fruit and seed production per inflorescence and increased aborted seeds per fruit. Resource addition to maternal plants significantly increased fruit and seed number in the field. Moreover, selfed plants exhibited greater variability in seed production in the absence of resource addition to the maternal plant. We planted a total of 1,306 of the seeds from this experiment in the greenhouse. While self-pollination did not affect the proportion of seeds emerging, it slowed seedling emergence by 5–10%, and reduced offspring biomass by 25–35%. Interestingly, resource addition to the maternal plants significantly decreased proportion of seedlings surviving after 5 months. Moreover, offspring from maternal plants with resource addition expressed more inbreeding depression in the seedling stage compared to offspring from maternal plants without resource addition, for which more inbreeding depression occurred during seed maturation and emergence. These results indicate that conservation efforts using benign environments to increase number of seeds or offspring may face compensating reductions in survivorship at other life stages.     

Island biogeography and the reproductive ecology of great tits Parus major

Island biogeography theory has contributed greatly to both theoretical and applied studies of conservation biology (e.g., design of nature reserves, minimum viable population sizes, extinction risk) and community composition. However, little theoretical and empirical work has addressed how island isolation and size affect reproductive ecology. We investigated the reproductive ecology of great tits (Parus major) on one offshore and one nearshore island, as well as on the Danish mainland. Tits breeding on the offshore island bred later, laid smaller clutches, and laid larger eggs than those on the nearshore island and mainland. In addition, the level of ectoparasite infestation in nests was highest on the offshore island, intermediate on the nearshore island, and lowest on the mainland. These insular effects may occur due to lower food abundance on islands, to density-dependent effects, or to effects related to low genetic diversity within island populations. Whatever the cause, the results emphasize that future studies of forest fragmentation/population isolation should consider not only gross measures of reproductive success, but also fine-scale measures such as clutch size, timing of breeding, and parasite prevalence. Received: 10 November 1997 / Accepted: 9 March 1998     

Environmental control of reproductive phenology and the effect of pollen supplementation on resource allocation in the cleistogamous weed, Ruellia nudiflora (Acanthaceae)

• Background and Aims Mixed reproductive strategies may have evolved as a response of plants to cope with environmental variation. One example of a mixed reproductive strategy is dimorphic cleistogamy, where a single plant produces closed, obligately self-pollinated (CL) flowers and open, potentially outcrossed (CH) flowers. Frequently, optimal environmental conditions favour production of more costly CH structures whilst economical and reliable CL structures are produced under less favourable conditions. In this study we explore (1) the effect of light and water on the reproductive phenology and (2) the effect of pollen supplementation on resource allocation to seeds in the cleistogamous weed Ruellia nudiflora.• Methods Split-plot field experiments were carried out to assess the effect of shade (two levels: ambient light vs. a reduction of 50 %) and watering (two levels: non-watered vs. watered) on the onset, end and duration of the production of three reproductive structures: CH flowers, CH fruit and CL fruit. We also looked at the effect of these environmental factors on biomass allocation to seeds (seed weight) from obligately self-pollinated flowers (CL), open-pollinated CH flowers and pollen-supplemented CH flowers.• Key Results CH structures were produced for a briefer period and ended earlier under shaded conditions. These conditions also resulted in an earlier production of CL fruit. Shaded conditions also produced greater biomass allocation to CH seeds receiving extra pollen.• Conclusions Sub-optimal (shaded) conditions resulted in a briefer production period of CH structures whilst these same conditions resulted in an earlier production of CL structures. However, under sub-optimal conditions, plants also allocated more resources to seeds sired from CH flowers receiving large pollen loads. Earlier production of reproductive structures and relatively larger seed might improve subsequent success of CL and pollen-supplemented CH seeds, respectively.     

Floral display, pollinator visitation and reproductive success in the dioecious perennial herb Wurmbea dioica (Liliaceae)

Floral traits that increase attractiveness to pollinators are predicted to evolve through selection on male function rather than on female function. To determine the importance of male-biased selection in dioecious Wurmbea dioica, we examined sexual dimorphism in flower size and number and the effects of these traits on pollinator visitation and reproductive success of male and female plants. Males produced more and larger flowers than did females. Bees and butterflies responded to this dimorphism and visited males more frequently than females, although flies did not differentiate between the sexes. Within sexes, insect pollinators made more visits to and visited more flowers on plants with many flowers. However, visits per flower did not vary with flower number, indicating that visitation was proportional to the number of flowers per plant. When flower number was experimentally held constant, visitation increased with flower size under sunny but not overcast conditions. Flower size but not number affected pollen removal per flower in males and deposition in females. In males, pollen removal increased with flower size 3 days after flowers opened, but not after 6 days when 98% of pollen was removed. Males with larger flowers therefore, may have higher fitness not because pollen removal is more complete, but because pollen is removed more rapidly providing opportunities to pre-empt ovules. In females, pollen deposition increased with flower size 3 days but not 6 days after flowers opened. At both times, deposition exceeded ovule production by four-fold or more, and for 2 years seed production was not limited by pollen. Flower size had no effect on seed production per plant and was negatively related to percent seed set, implying a tradeoff between allocation to attraction and reproductive success. This indicates that larger flower size in females is unlikely to increase fitness. In both sexes, gamete production was positively correlated with flower size. In males, greater pollen production would increase the advantage of large flowers, but in females more ovules may represent a resource cost. Selection to increase flower size and number in W. dioica has probably occurred through male rather than female function. Received: 15 June 1997 / Accepted: 12 February 1998     

Environmental regulation of the reproductive system in a flexibly breeding Sonoran Desert bird, the Rufous-winged Sparrow, Aimophila carpalis

We investigated reproductive regulation in male Rufous-winged Sparrows, Aimophila carpalis, a Sonoran Desert passerine that breeds after irregular summer rains. Field and captive data demonstrate that increased photoperiod stimulates testicular development in March and maintains it until early September. Free-living birds caught in July and placed on captive long days (16L: 8D) maintained developed testes for up to 7 months, and free-living birds caught in September, during testicular regression, redeveloped testes when placed on captive long days, indicating that these birds were still photosensitive. Captive birds on long days maintained testicular development when exposed to temperatures mimicking those occurring during regression in free-living birds. In free-living birds, testicular development was observed during spring and summer, but unless this was associated with rainfall, breeding (indicated by juveniles) did not occur. Large increases in plasma luteinizing hormone (LH) in free-living males were correlated with heavy rainfall in July/August, when the birds bred, and in November, when they did not breed. In captive birds, plasma LH concentrations were unresponsive to photoperiodic changes, but may have responded to social cues. Plasma prolactin concentrations were directly correlated with photoperiod in free-living birds, but an effect of photoperiod on prolactin secretion was not seen in captive birds. It is concluded that male Rufous-winged Sparrows use long photoperiods to stimulate and maintain testicular development, but exposure to long photoperiods does not terminate breeding by inducing absolute photorefractoriness. The specific timing of reproductive behaviors is apparently determined by elevated plasma LH coinciding with long day stimulated gonad development.     

Maternal reproductive decisions are independent of feeding in the black bean aphid,Aphis fabae

Aphids are phloem feeders and an important assumption has been that reproduction is initiated only after phloem ingestion. Here we investigate the plant tissue location of parturition cues in winged and wingless, summer virginoparae and autumn migrants (gynoparae) of the black bean aphid, Aphis fabae. These seasonal forms have different host preferences. Using electrical penetration graph (EPG: to observe activity of the mouthparts) and video-monitoring procedures we demonstrate that the time to first parturition after host-plant contact is significantly shorter than the time to first registered phloem contact in the summer winged form. In gynoparae, the time to first parturition does not significantly differ from time to first phloem contact but is shorter than time to first phloem ingestion. Times to first parturition, first registered phloem contact and first phloem ingestion do not differ significantly in the summer wingless form. Simultaneous EPG and video recording procedures show that a high proportion of individuals of all morphs (45-70%) initiate reproduction before sustained phloem activities (salivation/ingestion). The only behaviours that all individuals demonstrate before first parturition are ‘non-penetration’ (aphid on plant surface with mouthparts outside plant) and stylet ‘pathway activity’, including secretion of gelling saliva and penetration of the non-vascular (epidermis and mesophyll) cells. A short period of penetration of the peripheral plant tissues (five cell punctures per individual) by aphids tethered and monitored by EPG decreases the time to first parturition of the winged summer form when subsequently placed on a Parafilm sachet containing 15% sucrose solution. This treatment also significantly increases the incidence of reproduction and individual reproductive output of gynoparae over a 24-h period. No detectable effects of tissue penetration on subsequent reproductive output are observed in the wingless summer form. Additionally, EPGs reveal that a number of aphids of all morphs display xylem ingestion, which occurs predominantly before initiation of phloem feeding but is not necessary to initiate parturition. It is concluded that aphids are likely to detect parturition cues during stylet punctures of cells within peripheral tissue layers, before reaching the phloem vessels.     

Consequences of inbreeding for the cowpea seed beetle, Callosobruchus maculatus (F.)(Coleoptera: Bruchidae)

Inbreeding is said to reduce vigour and fitness. It may also determine how a population responds to selection. Local populations of Callosobruchus maculatus , the cowpea seed beetle, are established annually from small numbers of founders and the species has been distributed to many parts of the world where isolated populations may have been founded by very small numbers of individuals. After more than 20 generations of inbreeding, inbred lines have been shown to diverge from a common ancestral stock in similar directions with respect of some variables such as developmental speed, but haphazardly in respect of other parameters such as male weight. The respective roles of drift and of selection as effective evolutionary forces in inbred lines are discussed in the light of these results. It is argued that some intraspecific differences in C. maculatus may be explained as a product of periodic inbreeding, but that the process does not impair the ability to adapt to local conditions so contributing to the status of the species as a pest of international importance.