Changes In Breeding System Research Articles

Temporal and spatial differences in three-egg clutch frequency of the African Black Oystercatcher

African Black Oystercatchers Haematopus moquini produce a modal clutch size of two eggs and only rarely lay three eggs. A review of over 4 000 nest records from across their breeding range (dating back to the early 1960s) revealed that three-egg clutches have become more frequent, rising from 2% of recorded clutches before 1975 to >5% since 2000. Three-egg clutches are found predominantly in the south-western Cape and are clustered at specific sites in the region. They are produced earlier in the season compared to smaller clutch sizes and rarely occur after January. As this increase in three-egg clutch frequency is site specific, it might result from either a phenotypically plastic response to local resource availability, or a localised change in breeding system potentially resulting in more than one female laying in the same nest. While increased food availability might be the cause of changes in three-egg clutch frequencies, this is unlikely linked to the spread of the invasive mussel Mytilus galloprovincialis. Further research is needed to identify the cause of this phenomenon and evaluate how this change may affect the breeding success of this species.

Moving to mate: the evolution of separate and combined sexes in multicellular organisms

Which conditions favour the evolution of hermaphroditism or separate sexes? One classical hypothesis states that an organism's mode of locomotion (if any) when searching for a mate should influence breeding system evolution. We used published phylogenies to reconstruct evolutionary changes in adult mate-search efficiency and breeding systems among multicellular organisms. Employing maximum-likelihood analyses, we found that changes in adult mate-search efficiency are significantly correlated with changes in breeding system, and this result is robust to uncertainties in the phylogenies. These data provide the first statistical support, across a broad range of taxa, for the hypothesis that breeding systems and mate-search efficiency did not evolve independently. We discuss our results in context with other causal factors, such as inbreeding avoidance and sexual specialization, likely to affect breeding system evolution.

How and when did Arabidopsis thaliana become highly self‐fertilising

Changes in breeding system are a regular evolutionary change in plants, as self-fertilisation is often advantageous, particularly for weedy and colonising species. The adoption of Arabidopsis thaliana as a plant model species has led to interest in how self-incompatibility was lost so that this species became highly inbreeding. Molecular evolutionary approaches have recently focused on investigating two loci involved in the incompatibility recognition process in related Arabidopsis species; non-functional copies of these genes still exist in A. thaliana. New work studying polymorphism at these loci found strikingly low diversity at one of them, suggesting that spread of a mutation in this gene might have caused self-compatibility in an ancestor of A. thaliana. However, it is difficult to be sure of the time when the selfing habit evolved in the lineage that led to A. thaliana.

Genetic variation and evolution of Polaskia chichipe (Cactaceae) under domestication in the Tehuacán Valley, central Mexico

Polaskia chichipe is a columnar cactus under artificial selection in central Mexico because of its edible fruits. Our study explored the effect of human manipulation on levels and distribution of genetic variation in wild, silviculturally managed and cultivated sympatric populations. Total genetic variation, estimated in nine populations with five microsatellite loci, was H(T) = 0.658 +/- 0.026 SE, which was mainly distributed within populations (H(S) = 0.646) with low differentiation among them (F(ST) = 0.015). Fixation index (F(IS)) in all populations was positive, indicating a deficit of heterozygous individuals with respect to Hardy-Weinberg expectations. When populations were pooled by management type, the highest expected heterozygosity (H(E) = 0.631 +/- 0.031 SE) and the lowest fixation index (F(IS) = 0.07) were observed in wild populations, followed by cultivated populations (H(E) = 0.56 +/- 0.03 SE, F(IS) = 0.14), whereas the lowest variation was found in silviculturally managed populations (H(E) = 0.51 +/- 0.05 SE, F(IS) = 0.17). Low differentiation among populations under different management types (F(ST) 0.005, P < 0.04) was observed. A pattern of migration among neighbouring populations, suggested from isolation by distance (r2 = 0.314, P < 0.01), may have contributed to homogenizing populations and counteracting the effects of artificial selection. P. chichipe, used and managed for at least 700 generations, shows morphological differentiation, changes in breeding system and seed germination patterns associated with human management, with only slight genetic differences detected by neutral markers.

Effects of grazing disturbance on the reproduction of a perennial herb, Cypella herbertii (Lindl.) Herb. (Iridaceae)

A recent study in a natural grassland in Argentina revealed that grazing strongly reduced the available pollinators for a population of Cypella herbertii. Comparing grazed and fenced areas (exclosures) we tested the hypothesis that self-incompatibility would be selected against in a pollinator-poor environment leading to changes in breeding system. No differences in breeding system were found between populations from inside and outside exclosures. However, we detected: (i) C. herbertii clearly exhibits a mixed-mating system but has a remarkably low spontaneous fruit formation; (ii) this species though highly self-compatible expresses a significant decay at seed set stage when self-pollinated. We conclude that grazing impact on pollinators together with C. herbertii’s high dependence on pollinators should be considered when assessing the risk of extinction of this species.

Evolution of apomixis as a strategy of colonization in the dioecious species Lindera glauca (Lauraceae)

AbstractI have investigated the reproductive biology of four dioecious species of Lindera in Japan: Lindera obtusiloba Bl., L. umbellata Thunb., L. erythrocarpa Makino, and L. glauca Bl. The sex ratios in populations of the first three species are close to equality, but in L. glauca only female individuals are found in Japan, although males are known from continental Asia. The persistence of this dioecious species in the absence of males is surprising, and prompts the question: What mechanisms operate to ameliorate problems of colonization in species of Lindera? I carried out bagging experiments in order to test for apomixis (asexual reproduction by seeds) and to establish the importance of pollination and fertilization, and potential pollen vectors. Only L. glauca reproduced by apomixis. Level of fruit set was high, and was not affected by pollination. In the other three species, seed set was entirely dependent on pollen transfer, which could be accomplished by small Coleoptera and Diptera. The evolution of apomixis in L. glauca appears to have been a strategy to overcome sterility and establish a population in the Japanese islands even in the absence of males. However, this change in breeding system has not occurred in congeneric, co‐occurring species, which do not seem to have experienced a lack of male plants.

Testing kin selection with sex allocation data in eusocial hymenoptera

Sex allocation data in eusocial Hymenoptera (ants, bees and wasps) provide an excellent opportunity to assess the effectiveness of kin selection, because queens and workers differ in their relatedness to females and males. The first studies on sex allocation in eusocial Hymenoptera compared population sex investment ratios across species. Female-biased investment in monogyne (= with single-queen colonies) populations of ants suggested that workers manipulate sex allocation according to their higher relatedness to females than males (relatedness asymmetry). However, several factors may confound these comparisons across species. First, variation in relatedness asymmetry is typically associated with major changes in breeding system and life history that may also affect sex allocation. Secondly, the relative cost of females and males is difficult to estimate across sexually dimorphic taxa, such as ants. Thirdly, each species in the comparison may not represent an independent data point, because of phylogenetic relationships among species. Recently, stronger evidence that workers control sex allocation has been provided by intraspecific studies of sex ratio variation across colonies. In several species of eusocial Hymenoptera, colonies with high relatedness asymmetry produced mostly females, in contrast to colonies with low relatedness asymmetry which produced mostly males. Additional signs of worker control were found by investigating proximate mechanisms of sex ratio manipulation in ants and wasps. However, worker control is not always effective, and further manipulative experiments will be needed to disentangle the multiple evolutionary factors and processes affecting sex allocation in eusocial Hymenoptera.

Breeding systems and hybridization inPetrorhagia sect.Kohlrauschia (Caryophyllaceae)

In the diploid speciesP. prolifera, the evolution of autogamy has resulted in the presence of distinct selfing and outcrossing races. The change in breeding system toward autogamy is associated with a reduction in the size of floral features and a lower pollen production. The outbreeding populations have only been found in Greece, while the selfing populations have colonized much of Europe. The two races appear to be reproductively isolated from one another. —Petrorhagia sect.Kohlrauschia contains four species.P. glumacea is outbreeding and shows unilateral incompatibility with the small-flowered race ofP. prolifera and interfertility with the large-flowered race; althoughP. glumacea is sympatric with the large-flowered race, they do not appear to hybridize in the wild. Amongst the allopatric species, internal breeding barriers are also found. These may take the form of hybrid sterility or seed incompatibility.P. velutina is autogamous and reproductively isolated from all the other species of the section regardless of whether they are sympatric or allopatric. It is suggested that the evolution of autogamy has been an important factor in the spread ofP. velutina, the tetraploidP. nanteuilii, and the small-flowered race ofP. prolifera in Europe.

Flavonoids and Taxonomy of the Limnanthaceae

To help clarify relationships within the Limnanthaceae, all 19 taxa were compared on the basis of flavonoids occurring in all tissues, and 14 of these taxa were additionally compared on the basis of flavonoids occurring only in the petals. Of the 46 flavonol glycosides encountered, 35 were identified as derivatives of six flavonol aglycone types: syringetin, isorhamnetin, kaempferol, laricytrin (myricetin 3'-methyl ether), quercetin and myricetin, all glycosylated with combinations of glucose and rhamnose. Varimax Factor Analysis with rotation of the flavonoid data indicated that the family probably contains 3 phyletic lines, an observation inconsistent with the conventional 2-generic interpretation of the family. Mason's sectional treatment of Limnanthes is supported by petal flavonoid results, but not by whole-plant flavonoid results, indicating that petal flavonoids more clearly reflect natural relationships in Limnanthes. Evolution of whole-plant flavonoids of Limnanthes appears to be partly linked to changes in breeding system.

FLAVONOIDS AND TAXONOMY OF THE LIMNANTHACEAE

To help clarify relationships within the Limnanthaceae, all 19 taxa were compared on the basis of flavonoids occurring in all tissues, and 14 of these taxa were additionally compared on the basis of flavonoids occurring only in the petals. Of the 46 flavonol glycosides encountered, 35 were identified as derivatives of six flavonol aglycone types: syringetin, isorhamnetin, kaempferol, laricytrin (myricetin 3'‐methyl ether), quercetin and myricetin, all glycosylated with combinations of glucose and rhamnose. Varimax Factor Analysis with rotation of the flavonoid data indicated that the family probably contains 3 phyletic lines, an observation inconsistent with the conventional 2‐generic interpretation of the family. Mason's sectional treatment of Limnanthes is supported by petal flavonoid results, but not by whole‐plant flavonoid results, indicating that petal flavonoids more clearly reflect natural relationships in Limnanthes. Evolution of whole‐plant flavonoids of Limnanthes appears to be partly linked to changes in breeding system.

Cytogenetics and evolutionary change under domestication

Domesticated plants often show more striking variability at and below the species level than their wild relatives. Nevertheless, no unique processes have operated in crop plant evolution.The ultimate source of variation is mutation, which is then exposed to selection, natural or human. The direction of human selection may change through time and can usually be inferred only indirectly from archaeological artefacts. Where a crop is evolving in contact with its wild relatives, disruptive selection may lead to simultaneous divergence of crop and weed races. The crop may then become genetically isolated by change in breeding system, chromosome number or chromosome structure, though these processes are usually arrested short of total isolation or speciation. In crops that are grown on a garden rather than field scale, reproduce asexually, or have a long generation time, gene flow and disruptive selection are less significant, though human selection may be more intense.

EVOLUTIONARY RELATIONSHIPS IN THE OUTCROSSING DIPLOID ANNUAL SPECIES OF STEPHANOMERIA (COMPOSITAE).

The annual taxa of the western North American genus Stephanomeria (Compositae) provide excellent material for the comparative study of genetic differentiation and speciation in plants. They are a closely related assemblage, have broad and narrow distributions, occupy numerous habitats, and, in their center of variability in California, they are actively differentiating in response to sharp ecological gradients as well as the activities of man. They have long been known for their complex morphological intergradation (Ferris, 19660), which has stymied taxonomic efforts to separate the taxa. They exhibit a remarkable array of different evolutionary strategies involving changes in breeding system, polyploidy, hybridization, adaptation to particular substrates, and aggressive colonization of disturbed roadside habitats. As a result of the studies reported herein, the annual Stephanomerias are now known to include nine diploid (2n = 16) and two allotetraploid (2n = 32) taxa. Tetraploid chromosome numbers were first reported in Stephanomeria by Stebbins et al. (1953). They constitute both a polyploid complex and an homogamic complex in which the same divergent diploid species are connected by morphologically intermediate tetraploid and diploid species. Seven of the diploid taxa have a sporophytic selfincompatibility system and are consequently obligate outcrossers. The other two diploids and both tetraploids are selfcompatible and self-pollinating in the greenhouse. Their morphological, cyto-

Hybridity, polyploidy and change in breeding system in a Ruellia hybrid

Ruellia tweediana and R. tuberosa are large flowered chasmogamous diploids (n=17) with normal meiosis and fertility. F 1 hybrids, successful in only one direction (R. tweediana x R. tuberosa), are vegetatively vigorous and possess 17 often heteromorphic bivalents with high degree of segregational irregularities. It is exclusively cleistogamous and completely pollen and seed sterile. Like F 1, the artificial amphidiploid (n=34) is also cleistogamous but shows preferential chromosome pairing with complete restoration of fertility. The parental chromosomes are sufficiently differentiated and cleistogamy is either genie or due to gene-cytoplasm interaction but sterility is entirely chromosomal. All floral parts excepting calyx are highly deformed. Such a deformity is associated with sterility in the F 1 but with fertility in the amphidiploid. This is perhaps the first case of origin by hybridization of a true breeding and fully fertile cleistogamous taxon from two chasmogamous species. It also shows the extent and nature of change in breeding system brought about by hybridization and/or polyploidy.The chromosome numbers in the six, out of 16, obligate cleistogamous taxa (Table 4) show that they are high polyploids. Perhaps their origin has been in the same manner as in the present case.

Prevalence of self-incompatibility inOryza barthii Cheval.: Its bearing on the evolution of rice and related taxa

The prevalence of self-incompatibility inOryza barthii Cheval. and its implications on the origin of riceO. sativa L. and some other related taxa are discussed. It is suggested that evolution has been fromO. barthii toO. perennis toO. sativa with corresponding changes in breeding system from allogamy to facultative autogamy to obligate autogamy. The significance of the breeding system for speciation and evolutionary potentialities of these three taxa is pointed out. The presence inO. barthii of the most primitive characters of the genus and its widespread presence in tropical Africa (where nine out of 23 species of the genus occur) have been interpreted as suggesting that this region might have been the centre of origin of the genus.