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Article: Levels of inbreeding depression over seven generations of selfing in the androdioecious clam shrimp, Eulimnadia texana.

Weeks, S C

2004 Volume 17, Issue 3, Page(s) 475–484

Abstract: Androdioecy (mixtures of males and hermaphrodites) is a rare mating system in both plants and animals. Theory suggests that high levels of inbreeding depression can maintain males in androdioecious populations if hermaphrodites commonly self-fertilize. ... ...

Abstract	Androdioecy (mixtures of males and hermaphrodites) is a rare mating system in both plants and animals. Theory suggests that high levels of inbreeding depression can maintain males in androdioecious populations if hermaphrodites commonly self-fertilize. However, if inbreeding depression (delta) can be 'purged' from selfing populations, maintaining males is more difficult. In the androdioecious clam shrimp, Eulimnadia texana, delta is estimated to be as high as 0.7. Previous work suggests that this high level is maintained in the face of high levels of inbreeding due to an associative overdominance of fitness-related loci with the sex-determining locus. Such associative overdominance would make purging of inbreeding depression difficult to impossible. The current experiment was designed to determine if delta can be purged in these shrimp by tracking fitness across seven generations in selfing and outcrossing treatments. Evidence of purging was found in one of four populations, but the remaining populations demonstrated a consistent pattern of delta across generations. Although the experimental design allowed ample opportunity for purging, the majority of populations were unable to purge their genetic load. Therefore, delta in this species is likely due to associative overdominance caused by deleterious recessive alleles linked to the sex determining locus.
MeSH term(s)	Analysis of Variance ; Animals ; Crustacea/genetics ; Crustacea/physiology ; Disorders of Sex Development/genetics ; Genetics, Population ; Inbreeding ; Male ; Models, Biological ; Pedigree ; Sex Determination Processes ; Sexual Behavior, Animal/physiology
Language	English
Publishing date	2004-05
Publishing country	Switzerland
Document type	Comparative Study ; Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	1465318-7
ISSN	1420-9101 ; 1010-061X
ISSN (online)	1420-9101
ISSN	1010-061X
DOI	10.1111/j.1420-9101.2004.00712.x
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Article ; Online ; Research data: (with research data) A field test of a model for the stability of androdioecy in the freshwater shrimp, Eulimnadia texana.

Weeks, S C / Benvenuto, C / Reed, S K / Duff, R J / Duan, Z-H / David, P

Journal of evolutionary biology

2014 Volume 27, Issue 10, Page(s) 2080–2095

Abstract: The evolution of hermaphroditism from dioecy is a poorly studied transition. Androdioecy (the coexistence of males and hermaphrodites) has been suggested as an intermediate step in this evolutionary transition or could be a stable reproductive mode. ... ...

Abstract	The evolution of hermaphroditism from dioecy is a poorly studied transition. Androdioecy (the coexistence of males and hermaphrodites) has been suggested as an intermediate step in this evolutionary transition or could be a stable reproductive mode. Freshwater crustaceans in the genus Eulimnadia have reproduced via androdioecy for 24+ million years and thus are excellent organisms to test models of the stability of androdioecy. Two related models that allow for the stable maintenance of males and hermaphrodites rely on the counterbalancing of three life history parameters. We tested these models in the field over three field seasons and compared the results to previous laboratory estimates of these three parameters. Male and hermaphroditic ratios within years were not well predicted using either the simpler original model or a version of this model updated to account for differences between hermaphroditic types ('monogenic' and 'amphigenic' hermaphrodites). Using parameter estimates of the previous year to predict the next year's sex ratios revealed a much better fit to the original relative to the updated version of the model. Therefore, counter to expectations, accounting for differences between the two hermaphroditic types did not improve the fit of these models. At the moment, we lack strong evidence that the long-term maintenance of androdioecy in these crustaceans is the result of a balancing of life history parameters; other factors, such as metapopulation dynamics or evolutionary constraints, may better explain the 24+ million year maintenance of androdioecy in clam shrimp.
MeSH term(s)	Animals ; Biological Evolution ; Decapoda (Crustacea)/genetics ; Fresh Water ; Hermaphroditic Organisms/genetics ; Inbreeding ; Longevity ; Male ; Models, Biological ; Sex Ratio
Language	English
Publishing date	2014-10
Publishing country	Switzerland
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	1465318-7
ISSN	1420-9101 ; 1010-061X ; 1010-061X
ISSN (online)	1420-9101
ISSN	1010-061X
DOI	10.1111/jeb.12459
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Article: The effects of recurrent clonal formation on clonal invasion patterns and sexual persistence: a Monte Carlo simulation of the frozen niche-variation model.

Weeks, S C

The American naturalist

1993 Volume 141, Issue 3, Page(s) 409–427

Abstract: The interaction of sexual and asexual organisms in a heterogeneous environment was explored using a Monte Carlo simulation. The model was designed to address sexual persistence and the pattern of clonal invasion in a species that periodically produces ... ...

Abstract	The interaction of sexual and asexual organisms in a heterogeneous environment was explored using a Monte Carlo simulation. The model was designed to address sexual persistence and the pattern of clonal invasion in a species that periodically produces clonal mutants. The parameters of the model were the mutation rate of outcrossed sexuals to obligate asexuality, the number of progeny per parent, the within-genotype niche width, and the carrying capacity for nine separate resources. The inclusion of recurrent clonal invasion due to meiosis-disrupting mutations drove the sexual species extinct in temporally stable environments, at a rate dependent on the mutation frequency, sexual niche breadth, and the relative magnitude of the number of progeny per parent and the carrying capacity. In simulations with uniform resource distributions, clonal invasion was distinctly nonrandom. The pattern of clonal invasion was "centripetal'': mutant clones that captured or "froze" the rarely recombined (or marginal) sexual phenotypes were more successful initially than clones freezing frequently recombined (or central) sexual phenotypes. The long-term persistence of the sexuals was confined to simulations that included temporal resource fluctuations. In such instances, sexuals and asexuals coexisted in a mutation/extinction equilibrium, where asexuals were continually produced by mutation and lost by short-term random extinctions. Increased within-genotype niche width reduced the probability of clonal extinction and thus restricted the likelihood of sexual/clonal coexistence.
Language	English
Publishing date	1993-03
Publishing country	United States
Document type	Journal Article
ZDB-ID	207092-3
ISSN	1537-5323 ; 0003-0147
ISSN (online)	1537-5323
ISSN	0003-0147
DOI	10.1086/285481
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Article ; Online: Sex chromosome evolution in the clam shrimp, Eulimnadia texana.

Weeks, S C / Benvenuto, C / Sanderson, T F / Duff, R J

Journal of evolutionary biology

2010 Volume 23, Issue 5, Page(s) 1100–1106

Abstract: Chromosomes that determine sex are predicted to evolve differently than autosomes: a lack of recombination on one of the two sex chromosomes is predicted to allow an accumulation of deleterious alleles that eventually leads to reduced functionality and ... ...

Abstract	Chromosomes that determine sex are predicted to evolve differently than autosomes: a lack of recombination on one of the two sex chromosomes is predicted to allow an accumulation of deleterious alleles that eventually leads to reduced functionality and potential physical degradation of the nonrecombining chromosome. Because these changes should occur at an elevated evolutionary rate, it is difficult to find appropriate species in which to test these evolutionary predictions. The unique genetic sex-determining mechanism of the crustacean Eulimnadia texana prevents major chromosome degeneration because of expression of both 'proto-sex' (i.e. early stage of development) chromosomes in homozygous form (ZZ and WW). Herein, we exploit this unique genetic system to examine the predicted accumulation of deleterious alleles by comparing both homogametic sexual types to their heterogametic counterpart. We report differences in crossing over in a sex-linked region in the ZW hermaphrodites (approximately 3%) relative to the ZZ males (approximately 21%), indicative of cross-over suppression in the ZW hermaphrodites. Additionally, we report that both ZZ and WW genotypes have reduced fitness relative to ZW hermaphrodites, which is consistent with the prediction of harboured recessive mutations embedded on both the Z and the W chromosomes. These results suggest that the proto-sex chromosomes in E. texana accumulate recessive deleterious alleles. We hypothesize that recessive deleterious alleles of large effect cannot accumulate because of expression in both ZZ and WW individuals, keeping both chromosomes from losing significant function.
MeSH term(s)	Alleles ; Animals ; Crossing Over, Genetic/genetics ; DNA Primers/genetics ; Decapoda (Crustacea)/genetics ; Disorders of Sex Development ; Evolution, Molecular ; Female ; Genetic Fitness/genetics ; Genotype ; Male ; Microsatellite Repeats/genetics ; Sex Chromosomes/genetics
Chemical Substances	DNA Primers
Language	English
Publishing date	2010-05
Publishing country	Switzerland
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	1465318-7
ISSN	1420-9101 ; 1010-061X
ISSN (online)	1420-9101
ISSN	1010-061X
DOI	10.1111/j.1420-9101.2010.01963.x
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Article ; Research data: (with research data) A field test of a model for the stability of androdioecy in the freshwater shrimp, Eulimnadia texana

Weeks, S. C / Benvenuto, C / Reed, S. K / Duff, R. J / Duan, Z.‐H / David, P

Journal of evolutionary biology. 2014 Oct., v. 27, no. 10

2014

Abstract	The evolution of hermaphroditism from dioecy is a poorly studied transition. Androdioecy (the coexistence of males and hermaphrodites) has been suggested as an intermediate step in this evolutionary transition or could be a stable reproductive mode. Freshwater crustaceans in the genus Eulimnadia have reproduced via androdioecy for 24+ million years and thus are excellent organisms to test models of the stability of androdioecy. Two related models that allow for the stable maintenance of males and hermaphrodites rely on the counterbalancing of three life history parameters. We tested these models in the field over three field seasons and compared the results to previous laboratory estimates of these three parameters. Male and hermaphroditic ratios within years were not well predicted using either the simpler original model or a version of this model updated to account for differences between hermaphroditic types (‘monogenic’ and ‘amphigenic’ hermaphrodites). Using parameter estimates of the previous year to predict the next year's sex ratios revealed a much better fit to the original relative to the updated version of the model. Therefore, counter to expectations, accounting for differences between the two hermaphroditic types did not improve the fit of these models. At the moment, we lack strong evidence that the long‐term maintenance of androdioecy in these crustaceans is the result of a balancing of life history parameters; other factors, such as metapopulation dynamics or evolutionary constraints, may better explain the 24+ million year maintenance of androdioecy in clam shrimp.
Keywords	Crustacea ; androdioecy ; clams ; dioecy ; evolution ; freshwater ; hermaphroditism ; life history ; males ; models ; shrimp
Language	English
Dates of publication	2014-10
Size	p. 2080-2095.
Publishing place	Birkhäuser
Document type	Article ; Research data
ZDB-ID	1465318-7
ISSN	1420-9101 ; 1010-061X ; 1010-061X
ISSN (online)	1420-9101
ISSN	1010-061X
DOI	10.1111/jeb.12459
Database	NAL-Catalogue (AGRICOLA)

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Article: Sex chromosome evolution in the clam shrimp, Eulimnadia texana

WEEKS, S.C / BENVENUTO, C / SANDERSON, T.F / DUFF, R.J

Journal of evolutionary biology. 2010 May, v. 23, no. 5

2010

Abstract	Chromosomes that determine sex are predicted to evolve differently than autosomes: a lack of recombination on one of the two sex chromosomes is predicted to allow an accumulation of deleterious alleles that eventually leads to reduced functionality and potential physical degradation of the nonrecombining chromosome. Because these changes should occur at an elevated evolutionary rate, it is difficult to find appropriate species in which to test these evolutionary predictions. The unique genetic sex-determining mechanism of the crustacean Eulimnadia texana prevents major chromosome degeneration because of expression of both 'proto-sex' (i.e. early stage of development) chromosomes in homozygous form (ZZ and WW). Herein, we exploit this unique genetic system to examine the predicted accumulation of deleterious alleles by comparing both homogametic sexual types to their heterogametic counterpart. We report differences in crossing over in a sex-linked region in the ZW hermaphrodites (~ 3%) relative to the ZZ males (~ 21%), indicative of cross-over suppression in the ZW hermaphrodites. Additionally, we report that both ZZ and WW genotypes have reduced fitness relative to ZW hermaphrodites, which is consistent with the prediction of harboured recessive mutations embedded on both the Z and the W chromosomes. These results suggest that the proto-sex chromosomes in E. texana accumulate recessive deleterious alleles. We hypothesize that recessive deleterious alleles of large effect cannot accumulate because of expression in both ZZ and WW individuals, keeping both chromosomes from losing significant function.
Keywords	androdioecy ; Crustacea
Language	English
Dates of publication	2010-05
Size	p. 1100-1106.
Publisher	Blackwell Publishing Ltd
Publishing place	Oxford, UK
Document type	Article
ZDB-ID	1465318-7
ISSN	1420-9101 ; 1010-061X
ISSN (online)	1420-9101
ISSN	1010-061X
DOI	10.1111/j.1420-9101.2010.01963.x
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Article: Phenotypic plasticity of live-history traits in clonal and sexual fish (Poeciliopsis) at high and low densities

Weeks, S.C.

Oecologia (Germany)

1993

Abstract: Models of resource allocation strategies predict an array of life- history responses of individuals living in resource-stressed versus non-stressed environments. I tested a number of these predictions using three fish strains (a sexual and two clonal ... ...

Institution	Rutgers the State Univ., New Brunswick, NJ (USA). Cook College. Center for Theorethical and Applied Genetics
Abstract	Models of resource allocation strategies predict an array of life- history responses of individuals living in resource-stressed versus non-stressed environments. I tested a number of these predictions using three fish strains (a sexual and two clonal strains) in high and low density treatments. To examine the plasticity of life-history traits in females raised in these two environments, I measured survi- val, growth, egg production, egg size, and proportion mature at 10 weeks of age. Survival was not affected by density treatment. Howe- ver, both growth and overall egg production were lower in femals from the high density treatments, and reproductive maturity was signifi- cantly delayed at the high density for all strains. Egg production per unit size was not affected by density in any strain, signifying that differences in the numbers of eggs produced was merely a reflec- tion of the differences in size of fish in the two density treat- ments. Egg size was also unaffected by density in all strains. These results are related to models of resource allocation in stressful environments. There was a consistent pattern of increased reproducti- ve investment in the sexual strain relative to the two clonal strains. The sexual strain matured earlier, produced more eggs per unit body weight, and had larger eggs than either clone at both densities. These results are interpreted by considering the predicted adaptive responses of these three strains to the long-term environ- mental differnces in their natural habitats.
Keywords	Growth ; Reproduction ; Fish ; Phenotypes
Language	English
Edition	v. 93(3) p. 307-314
Document type	Article
ISSN	0029-8549
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Article ; Online: Evolutionary transitions among dioecy, androdioecy and hermaphroditism in limnadiid clam shrimp (Branchiopoda: Spinicaudata).

Weeks, S C / Chapman, E G / Rogers, D C / Senyo, D M / Hoeh, W R

Journal of evolutionary biology

2009 Volume 22, Issue 9, Page(s) 1781–1799

Abstract: Examinations of breeding system transitions have primarily concentrated on the transition from hermaphroditism to dioecy, likely because of the preponderance of this transition within flowering plants. Fewer studies have considered the reverse transition: ...

Abstract	Examinations of breeding system transitions have primarily concentrated on the transition from hermaphroditism to dioecy, likely because of the preponderance of this transition within flowering plants. Fewer studies have considered the reverse transition: dioecy to hermaphroditism. A fruitful approach to studying this latter transition can be sought by studying clades in which transitions between dioecy and hermaphroditism have occurred multiple times. Freshwater crustaceans in the family Limnadiidae comprise dioecious, hermaphroditic and androdioecious (males + hermaphrodites) species, and thus this family represents an excellent model system for the assessment of the evolutionary transitions between these related breeding systems. Herein we report a phylogenetic assessment of breeding system transitions within the family using a total evidence comparative approach. We find that dioecy is the ancestral breeding system for the Limnadiidae and that a minimum of two independent transitions from dioecy to hermaphroditism occurred within this family, leading to (1) a Holarctic, all-hermaphrodite species, Limnadia lenticularis and (2) mixtures of hermaphrodites and males in the genus Eulimnadia. Both hermaphroditic derivatives are essentially females with only a small amount of energy allocated to male function. Within Eulimnadia, we find several all-hermaphrodite populations/species that have been independently derived at least twice from androdioecious progenitors within this genus. We discuss two adaptive (based on the notion of 'reproductive assurance') and one nonadaptive explanations for the derivation of all-hermaphroditism from androdioecy. We propose that L. lenticularis likely represents an all-hermaphrodite species that was derived from an androdioecious ancestor, much like the all-hermaphrodite populations derived from androdioecy currently observed within the Eulimnadia. Finally, we note that the proposed hypotheses for the dioecy to hermaphroditism transition are unable to explain the derivation of a fully functional, outcrossing hermaphroditic species from a dioecious progenitor.
MeSH term(s)	Animals ; Crustacea/genetics ; Disorders of Sex Development ; Female ; Male ; Phylogeny ; Sex Determination Processes
Language	English
Publishing date	2009-09
Publishing country	Switzerland
Document type	Comparative Study ; Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	1465318-7
ISSN	1420-9101 ; 1010-061X
ISSN (online)	1420-9101
ISSN	1010-061X
DOI	10.1111/j.1420-9101.2009.01813.x
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Article ; Online: Relative fitness of two hermaphroditic mating types in the androdioecious clam shrimp, Eulimnadia texana.

Weeks, S C / Crosser, B R / Gray, M M

Journal of evolutionary biology

2001 Volume 14, Issue 1, Page(s) 83–94

Abstract: Androdioecy (populations of males and hermaphrodites) is a rare reproductive form, being described from only a handful of plants and animals. One of these is the shrimp Eulimnadia texana, which has populations comprised of three mating types: two ... ...

Abstract	Androdioecy (populations of males and hermaphrodites) is a rare reproductive form, being described from only a handful of plants and animals. One of these is the shrimp Eulimnadia texana, which has populations comprised of three mating types: two hermaphroditic types (monogenics and amphigenics) and males. In a recent study, the amphigenic hermaphrodites were found to be in greater abundance than that predicted from a model of this mating system. Herein, we compare the relative fitness of offspring from amphigenic and monogenic siblings, attempting to understand the greater relative abundance of the former. Populations started with offspring from selfed monogenic hermaphrodites had a net reproductive rate (R) 87% that of offspring from their amphigenic siblings. Additionally, within populations of amphigenic offspring (which included males, monogenics and amphigenics), amphigenics survived longer than monogenics. These differences help to explain the increased relative abundance of amphigenics in natural populations, but amphigenics continue to be more abundant than expected.
Language	English
Publishing date	2001-01-08
Publishing country	Switzerland
Document type	Journal Article
ZDB-ID	1465318-7
ISSN	1420-9101 ; 1010-061X
ISSN (online)	1420-9101
ISSN	1010-061X
DOI	10.1046/j.1420-9101.2001.00251.x
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Article: The genetic mechanism of sex determination in the conchostracan shrimp Eulimnadia texana.

Sassaman, C / Weeks, S C

The American naturalist

1993 Volume 141, Issue 2, Page(s) 314–328

Abstract: We report the results of a laboratory pedigree analysis describing the unique sex-determining mechanism of the conchostracan shrimp, Eulimnadia texana. Natural populations of E. texana are mixtures of self-compatible hermaphrodites and males and ... ...

Abstract	We report the results of a laboratory pedigree analysis describing the unique sex-determining mechanism of the conchostracan shrimp, Eulimnadia texana. Natural populations of E. texana are mixtures of self-compatible hermaphrodites and males and represent one of the few known cases of androdioecy in animals. Hermaphrodites are of two types: amphigenic (producing both male and hermaphroditic offspring) and monogenic (producing only hermaphroditic offspring). We propose a simple genetic model to explain this polymorphism and show by genetic analysis that males, amphigenics, and monogenics can be interpreted as three alternative phenotypes of a one-locus system of sex determination. We discuss the implications of this novel system of sex determination for understanding the evolution of reproductive systems.
Language	English
Publishing date	1993-02
Publishing country	United States
Document type	Journal Article
ZDB-ID	207092-3
ISSN	1537-5323 ; 0003-0147
ISSN (online)	1537-5323
ISSN	0003-0147
DOI	10.1086/285475
Database	MEDical Literature Analysis and Retrieval System OnLINE

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