The dominant and ancestral mode of sex determination in the Hymenoptera is arrhenotokous parthenogenesis, in which diploid females develop from fertilized eggs and haploid males develop from unfertilized eggs. We discuss recent progress in the understanding of the genetic and cytoplasmic mechanisms that make arrhenotoky possible. The best-understood mode of sex determination in the Hymenoptera is complementary sex determination (CSD), in which diploid males are produced under conditions of inbreeding. The gene mediating CSD has recently been cloned in the honey bee and has been named the complementary sex determiner. However, CSD is only known from 4 of 21 hymenopteran superfamilies, with some taxa showing clear evidence of the absence of CSD. Sex determination in the model hymenopteran Nasonia vitripennis does not involve CSD, but it is consistent with a form of genomic imprinting in which activation of the female developmental pathway requires paternally derived genes. Some other hymenopterans are not arrhenotokous but instead exhibit thelytoky or paternal genome elimination.

Sex Determination in the Hymenoptera

Excluding insects, hermaphroditism occurs in about one-third of animal species, providing numerous opportunities for the evolution of selfing. Here we provide an overview of reproductive traits in hermaphroditic animal species, review the distribution of selfing rates in animals, and test for ecological correlates of selfing. Our dataset (1342 selfing-rate estimates for 142 species) is 97% based on estimates derived from the analysis of population structure (FIS-estimates) using genetic markers. The distribution of selfing is slightly &#x1d5e8;-shaped and differs significantly from the more strongly &#x1d5e8;-shaped plant distribution with 47% of animal t-estimates being intermediate (falling between 0.2 and 0.8) compared to 42% for plants. The influence of several factors on the distribution of selfing rates was explored (e.g., number of populations studied per species, habitat, coloniality, sessility, or fertilization type), none of which significantly affect the distribution. Our results suggest that genetic ...

https://bioone.org/journals/evolution/volume-60/issue-9/06-246.1/ANIMALS-MIX-IT-UP-TOO--THE-DISTRIBUTION-OF-SELF/10.1554/06-246.1.pdf

Animals mix it up too: the distribution of self-fertilization among hermaphroditic animals

The haplodiploid sex determining mechanism in Hymenoptera (males are haploid, females are diploid) has played an important role in the evolution of this insect order. In Hymenoptera sex is usually determined by a single locus, heterozygotes are female and hemizygotes are male. Under inbreeding, homozygous diploid and sterile males occur which form a genetic burden for a population. We review life history and genetical traits that may overcome the disadvantages of single locus complementary sex determination (sl-CSD). Behavioural adaptations to avoid matings between relatives include active dispersal from natal patches and mating preferences for non-relatives. In non-social species, temporal and spatial segregation of male and female offspring reduces the burden of sl-CSD. In social species, diploid males are produced at the expense of workers and female reproductives. In some social species, diploid males and diploid male producing queens are killed by workers. Diploid male production may have played a role in the evolution or maintenance of polygyny (multiple queens) and polyandry (multiple mating). Some forms of thelytoky (parthenogenetic female production) increase homozygosity and are therefore incompatible with sl-CSD. We discuss a number of hypothetical adaptations to sl-CSD which should be considered in future studies of this insect order.

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Single locus complementary sex determination in Hymenoptera: an "unintelligent" design?

Many organisms have the ability to shed an appendage (autotomy) to escape a predator or fouled molting event. Despite its immediate advantage on survivorship, autotomy can have important consequences for locomotion, foraging, survivorship, and/ or reproduction. Thus, regeneration is a way that animals alleviate some of the costs associated with losing an appendage. Like autotomy, however, appendage regeneration can have important consequences for a variety of aspects of fitness; in a wide range of amphibians, reptiles, fishes, and arthropods, the allocation of resources to regenerate a lost appendage negatively affects somatic or reproductive growth. Previous research into the costs associated with regeneration has provided a strong framework to explore how trade-offs associated with regeneration may have influenced its evolution. However, all research to date describing the costs and benefits associated with autotomy and regeneration have compared individuals autotomizing and regenerating an appendage with individuals that have never lost an appendage. I suggest that for studies of the evolutionary significance of regeneration, an alternative comparison is between individuals experiencing autotomy without regeneration and individuals experiencing autotomy with regeneration. Future work in this direction promises new insights into the evolution of regenerative tendencies, as well as how regeneration may be influencing animal form and function. Key words: autotomy, costs, evolution, regeneration, trade-offs. [Behav Ecol]

/pdf/the-costs-of-autotomy-and-regeneration-in-animals-a-review-51qizyufx3.pdf

The costs of autotomy and regeneration in animals: a review and framework for future research

There are three major classes of insect genetic systems: those with diploid males (diplodiploidy), those with effectively haploid males (haplodiploidy), and those without males (thelytoky). Mixed systems, involving cyclic or facultative switching between thelytoky and either of the other systems, also occur. I present a classification of the genetic systems of insects and estimate the number of evolutionary transitions between them that have occurred. Obligate thelytoky has arisen from each of the other systems, and there is evidence that over 900 such origins have occurred. The number of origins of facultative thelytoky and the number of reversions from obligate thelytoky to facultative and cyclic thelytoky are difficult to estimate. The other transitions are few in number: five origins of cyclic thelytoky, eight origins of obligate haplodiploidy (including paternal genome elimination), the strange case of Micromalthus, and the two reversions from haplodiploidy to diplodiploidy in scale insects. Available evidence tends to support W.D. Hamilton's hypothesis that maternally transmitted endosymbionts have been involved in the origins of haplodiploidy. Bizarre systems of extrazygotic inheritance in Sternorrhyncha are not easily accommodated into any existing classification of genetic systems.

The evolution of alternative genetic systems in insects

Publisher Summary This chapter discusses the morphology and cytology of the accessory sex glands in invertebrates. Gland cells secreting chemically different molecules have been grouped either vertically, each type of gland spatially sufficiently separated from the others and specialized to produce a specific secretion or horizontally, with different secretions being produced by different cells in the same glandular epithelium or by the same cells with or without temporal succession. The complexity of the secretory behavior is well illustrated by L. nuttalli in which the first pair of accessory sex glands of the male produces six different secretions, all of which are used in spermatophore formation. The chapter explains how the secretory apparatus of accessory sex gland cells is modified to produce their characteristic secretions. Gland cells that look alike morphologically may produce different secretions, for example, the ejaculatory duct epithelial cells of Musca secrete at least 12 proteins. A degree of plasticity in the activity of the secretory apparatus may be expected only in these multipotent cells. Accessory sex gland function being indispensable for successful reproduction in nearly all advanced animal groups, it is indeed surprising that correlative studies on the structure, biochemistry, and physiology of the accessory glandular elements are comparatively few.

Morphology and Cytology of the Accessory Sex Glands in Invertebrates

Reproductive biology of invertebrates. Volume IV. Part A. Fertilization, development, and parental care.

Comparative physiology of reproduction in arthropods.

Summary In adult males of the freshwater crab Paratelphusa hydrodromous, judging from testicular activity, November-May is the reproductively inactive season and June/July through October the active season. The reproductively active period also represents the mating season of this species. In males over one year old, moulting is an annual event scheduled during June/July and the individual remains in intermoult from July/August to May. This intermoult comprises two phases: (1) the reproductive phase (July/August through October) when the physiological emphasis is more on reproduction and much less on somatic growth (as evidenced by the ability to regenerate autotomized walking limb), (2) the somatic phase (February/March through May) when the emphasis is more on somatic growth and much less on reproduction. Thus there exists an antagonism between reproduction and somatic grown in male P. hydrodromous as already established in the female. Experimental studies suggest that the testicular inactive phase of P...

The antagonism between somatic growth and testicular activity during different phases in intermoult (stage C4) in sexually mature freshwater crab, Paratelphusa hydrodromous

R. G. Adiyodi

Papers

Morphology and Cytology of the Accessory Sex Glands in Invertebrates

Reproductive biology of invertebrates. Volume IV. Part A. Fertilization, development, and parental care.

Comparative physiology of reproduction in arthropods.

The antagonism between somatic growth and testicular activity during different phases in intermoult (stage C4) in sexually mature freshwater crab, Paratelphusa hydrodromous

Microorganism-induced parthenogenesis.