Maintenance Of Androdioecy Research Articles

Digest: Evolution and maintenance of androdioecy in a haplodiploid insect.

The coexistence of hermaphrodites and males (androdioecy) is rare in both plants and animals and has hitherto remained unknown in insects. Mongue etal. report a new case of androdioecy in the invasive haplodiploid insect Icerya purchasi, in which hermaphrodites can only self-fertilize, but occasionally mate with males. Revealingly, I. purchasi shares several features with other androdioecious species such as the consequences of evolution from separate sexes, low outcrossing rates, and its colonizing habit.

Functional androdioecy in the ornamental shrub Osmanthus delavayi (Oleaceae).

Androdioecy is one of the rarest sexual systems among plants, characterized by males co-occurring with hermaphrodites. Osmanthus delavayi (Oleaceae), an ornamental shrub from southern China, is known to have both male and hermaphrodite individuals, but little is known regarding the breeding system of this species and whether it is functionally androdioecious, and how this potentially evolved. In this study, we explore the characteristics of the breeding system of O. delavayi through the study of phenology, sex ratio, floral organ morphology, pollen number, stigma receptivity, artificial pollination, pollinators, and gene flow within and between populations, while also discussing the evolution and maintenance of androdioecy within the genus. The proportion of males was less than 0.5 and the out-crossing index (OCI) was 5. Morphological androdioecy was observed, with hermaphrodite flowers having fertile pistils, while male flowers had degenerated pistils. Males and hermaphrodites both had large amounts of small and fertile pollen grains, although the pollen number of males was ca. 1.21 × more than that of hermaphrodites, and pollen was generally smaller. Self-pollination was found to produce a much lower fruit set than outcrossing under natural conditions. Gene flow between males and hermaphrodites within a population was greater (1.007) than that between populations (0.753). All these results indicate that O. delavayi is functionally androdioecious, which may be an intermediate state in the evolutionary transition from hermaphroditism to dioecy.

Functional androdioecy in the rare endemic treeTapiscia sinensis

Tapiscia sinensis, a rare endemic woody plant with both male and hermaphrodite individuals, is distributed in southern China. Whether T. sinensis is functionally androdioecious is unknown. In this study, we compare the male fitness between male and hermaphrodite individuals and perform pollination experiments in different habitats, identify the ability of actual siring of pollen from hermaphrodites and males under natural pollination, and discuss the evolution and maintenance of androdioecy in T. sinensis. Research suggests that flowers and fruits grow synchronously on hermaphrodite plants of T. sinensis from April to June. The males of T. sinensis had more than twice the genetic contribution of hermaphrodites through their male function and the fruit set from male pollination and cross-pollination was the highest in all of the treatments, whereas that from self-pollination was the lowest. Additionally, paternity analysis showed that the hermaphroditic pollen could result in siring success under natural pollination. The results showed that T. sinensis is a functionally androdioecious tree, that male individuals might evolve from a hermaphroditic ancestor and that the synchronous growth of flowers and fruit in hermaphrodites might facilitate the evolution and maintenance of androdioecy in T. sinensis.

The joint evolution and maintenance of self-incompatibility with gynodioecy or androdioecy.

Mating systems show two kinds of frequent transitions: from hermaphroditism to dioecy, gynodioecy or androdioecy, or from self-incompatibility (SI) to self-compatibility (SC). While models have mostly investigated these two kinds of transitions as independent, empirical observations suggest that, to some extent, they can evolve jointly. Here, we study the joint evolution and maintenance of SI and androdioecy or SI and gynodioecy by the means of phenotypic models. Our models focus on three parameters: the unisexuals׳ advantage relative to that of the hermaphrodites due to resource reallocation, inbreeding depression and the selfing rate. We assume no pollen limitation or discounting. We show that SI helps the maintenance of androdioecy, but favors the loss of gynodioecy, and also that androdioecy facilitates the maintenance of SI, whereas gynodioecy does not affect it. We finally investigate how gynodioecy and androdioecy may affect the diversification of SI groups, especially considering an evolutionary pathway through SC intermediates. We show that while androdioecy prevents the increase of the number of SI groups, under certain conditions of inbreeding depression and selfing rates, gynodioecy allows it.

The Evolution and Maintenance of Androdioecy

▪ Abstract Examples of androdioecy, the coexistence of males and hermaphrodites, was unknown when the subject was last reviewed about two decades ago. Since then, several examples have been discovered in both plants and animals, and we are now in a position to reappraise theoretical work on the subject. Whereas early ideas were framed largely in terms of the invasion of males into hermaphroditic populations, all of the clearest examples of androdioecy now known appear to have evolved from dioecy. There are strong indications that this has occurred repeatedly as a result of the selection of self-fertile hermaphroditism for reproductive assurance during colonization. Male frequencies in these species are highly variable, self-fertilization in hermaphrodites is delayed, and mating opportunities appear to depend strongly on population density. Results from theoretical work on the evolution and maintenance of androdioecy in single populations and in metapopulations are summarized, and several case studies of androdioecious plants and animals are reviewed.

Maintenance of androdioecy in the freshwater shrimp Eulimnadia texana: sexual encounter rates and outcrossing success

The clam shrimp Eulimnadia texana has a rare mating system known as androdioecy, in which males and hermaphrodites cooccur but there are no pure females. In this species, reproduction takes place by outcrossing between males and hermaphrodites, or by selfing within a hermaphrodite; this system provides a unique opportunity to examine the adaptive significance of outcrossing and selfing in animals. Our study examined mating behavior in hermaphrodites and males from two populations to understand the propensity of these shrimp to mate and to estimate a parameter of a model developed by Otto et al. (American Naturalist 141:329–337), which predicts the conditions for stability of the mixed mating system in E. texana. Here we present evidence that mating frequency is environmentally sensitive, with greater numbers of encounters and matings per male when males are rare and in younger males. However, the effects of shrimp density, relative male frequency, and shrimp age interact in a complex way to determine male mating success. Overall, mating frequency was determined by a combination of encounter rates between the sexes and the proportion of encounters resulting in mating. The mating rates were then used to estimate one of four parameters of the Otto et al. model, and these estimates were combined with previous estimates of the other three parameters to examine the fit of the predicted to the observed sex ratios in the two populations. Key words: androdioecy, branchiopod crustaceans, evolution of breeding systems, inbreeding, mating success, mating tactics, mixed mating system, selffertilization. [Behav Ecol 13:561–570 (2002)]

Maintenance of androdioecy in the freshwater shrimp, Eulimnadia texana: do hermaphrodites need males for complete fertilization?

Androdioecy (populations comprised of mixtures of males and hermaphrodites) is a rare mating system, found only in a few plants and animals. The rarity of this system stems from the limited benefits to males in an otherwise all-hermaphroditic population. One of the potential benefits to males is typified by the nematode Caenorhabditis elegans, in which hermaphrodites do not produce sufficient sperm to fertilize all of their eggs. Here we explore the possibility that males are needed for complete fertilization of hermaphrodites' eggs in a second androdioecious animal, the clam shrimp Eulimnadia texana. We compare the fertilization rate of outcrossed to selfed eggs to test whether the latter exhibit lower fertilization due to sperm limitation (as in C. elegans). Because this comparison confounds differences in egg fertilization due to sperm limitation with the potential for early inbreeding depression, we also used a third mating treatment, a brother/sister cross, to allow separation of sperm limitation from inbreeding depression. In both populations examined, the proportion of eggs that were fertilized decreased linearly with increasing relatedness: comparing eggs produced by outcrossing, brother/sister, and selfed matings, respectively. This pattern suggests that differences in fertilization among these three treatments were caused solely by inbreeding depression, and therefore that hermaphrodites are not sperm limited. These results are combined with previous data on this species to test whether the maintenance of males can be explained using a population genetics model specifically designed for this species.

Reproductive biology of Phillyrea angustifolia L. (Oleaceae) and effect of galling-insects on its reproductive output

Abstract The breeding system of Phillyrea angustifolia is examined in several Spanish populations, both in the southeastern Iberian Peninsula and in the Balearic Islands. Hand-pollination experiments performed on one of the mainland and on one of the island populations demonstrated that the plant is functionally androdioecious. Pollen from males was several times more fertile than pollen from hermaphrodite flowers or self-pollen in the island population, but not so in the Iberian Peninsula. The interpretation of such a result is that androdioecy must have an adaptive advantage in an island system, where inbreeding depression is expected to be greater. Male individuals are much less common than hermaphrodites in all populations studied, thus supporting the prediction made by the models for the maintenance of androdioecy. Sex expression in an individual plant differs between populations. The frequency of sexes was purely bimodal in one population, whereas it was not so in another. Pollen from both male and hermaphrodite flowers appears to be morphologically different, although it remains unknown at what stage of the fertilization process the difference becomes functional. Fruitset in the hermaphrodite individuals was always less than 10%. Most fruits abort at an early stage and there is also a great flower abscission. Fruitset does not appear to be influenced by any of the plant traits describing size or fecundity. A high unpredictability of flowering in an individual was also observed in all populations. P. angustifolia is attacked by a cecidomyiid fly that induces the formation of galls in the ovaries (producing 'deformed' fruits which have been confused until recently with parthenocarpic fruits), thus reducing the plant reproductive output. The production of such galls (most of them in the hermaphrodite individuals but a small proportion also in males) is highly variable among plants and among populations, representing from 0 to 97% of the initiated fruits. Such variability in gall incidence does not respond to variability in plant size, fecundity, distance to flowering conspecifics or time that flowers are available for fly oviposition. A high consistency in gall production was found in both the mainland and the island populations. The greater abundance of galls in the islands compared with the mainland populations is interpreted as a result of the higher temperatures in the former which might influence the activity period of the flies.