So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

1. Introductory remarks 2. Convolvulacaea 2. Scrophulariaceae, Gesneriaceae, Labiatae, etc. 4. Cruciferae, Papaveraceae, Resedaceae, etc. 5. Geraniaceae, Leguminosae, Onagraceae, etc. 6. Solanaceae, Primulaceae, Polygoneae, etc. 7. Summary of the heights and weights of the crossed and self-fertilised plants 8. Difference between crossed and self-fertilised plants in constitutional vigour and in other respects 9. The effects of cross-fertilisation and self-fertilisation on the production of seeds 10. Means of fertilisation 11. The habits of insects in relation to the fertilisation of flowers 12. General results Index.

The Effects of Cross and Self Fertilisation in the Vegetable Kingdom: CONVOLVULACEÆ

Clearly, the possibility that Van Peenen's statements are correct exists, but no molecular geneticist would contend that these assertions have been established, in any but a very few cases, which appear at present to be atypical. The educated lavman, for whom this book is intended, will find the author's leaps from the level of the quoted material into sophisticated physical chemistry and back again disconcerting at least, if not completely confusing. It can be said, however, that the authors have assembled an excellent group of illustrations; lecturers in elementary genetics wishing to locate clear illustrations to use as slides would do well to look in this book first.

Animal Tissue Techniques.

Population connectivity plays significant roles on both evolutionary and ecological time-scales; however, quantifying the magnitude and pattern of ex- change between populations of marine organisms is hindered by the difficulty of tracking the trajectory and fate of propagules. We explored biophysical correlates of population substructure to determine how well pelagic larval duration (PLD) correlates with population genetic estimates of connectivity in a sample of 300 published studies drawn pseudo-randomly from about 1600 hits on electronic searches. In direct contrast to the general expectation of a strong correlation, we find that average PLD is poorly correlated (r 2 < 0.1) with genetic structure (FST). Furthermore, even this weak correlation is anchored by non-pelagic dispersal, because removal of the zero PLD class (direct developers) from the analy- sis resulted in a non-significant relationship between FST and PLD. For species in which minimum, maximum, and mean PLDs were available, it is noteworthy that both minimum and maximum PLDs are better corre- lated with FST than the mean larval duration, which has been used in all such previous studies. A 3-way AN- COVA reveals that genetic marker class (allozymes, microsatellites, and mitochondrial DNA sequences), as opposed to habitat or swimming ability, explain most of the variation in FST (F = 7.113, df = 2, p = 0.001), with higher values of FST obtained from mtDNA than with either microsatellites or allozymes (which were not sig- nificantly different). Our meta-analysis refutes recent reviews and conventional wisdom that PLD is a good predictor of the magnitude of gene flow and geo- graphic scale of population structure in marine systems.

/pdf/population-genetics-larval-dispersal-and-connectivity-in-148msamk1s.pdf

Population genetics, larval dispersal, and connectivity in marine systems

Genomic scans of multiple populations often reveal marker loci with greatly increased differentiation between populations. Often this differentiation coincides in space with contrasts in ecological factors, forming a genetic–environment association (GEA). GEAs imply a role for local adaptation, and so it is tempting to conclude that the strongly differentiated markers are themselves under ecologically based divergent selection, or are closely linked to loci under such selection. Here, we highlight an alternative and neglected explanation: intrinsic (i.e. environment-independent) pre- or post-zygotic genetic incompatibilities rather than local adaptation can be responsible for increased differentiation. Intrinsic genetic incompatibilities create endogenous barriers to gene flow, also known as tension zones, whose location can shift over time. However, tension zones have a tendency to become trapped by, and therefore to coincide with, exogenous barriers due to ecological selection. This coupling of endogenous and exogenous barriers can occur easily in spatially subdivided populations, even if the loci involved are unlinked. The result is that local adaptation explains where genetic breaks are positioned, but not necessarily their existence, which can be best explained by endogenous incompatibilities. More precisely, we show that (i) the coupling of endogenous and exogenous barriers can easily occur even when ecological selection is weak; (ii) when environmental heterogeneity is fine-grained, GEAs can emerge at incompatibility loci, but only locally, in places where habitats and gene pools are sufficiently intermingled to maintain linkage disequilibria between genetic incompatibilities, local-adaptation genes and neutral loci. Furthermore, the association between the locally adapted and intrinsically incompatible alleles (i.e. the sign of linkage disequilibrium between endogenous and exogenous loci) is arbitrary and can form in either direction. Reviewing results from the literature, we find that many predictions of our model are supported, including endogenous genetic barriers that coincide with environmental boundaries, local GEA in mosaic hybrid zones, and inverted or modified GEAs at distant locations. We argue that endogenous genetic barriers are often more likely than local adaptation to explain the majority of Fst-outlying loci observed in genome scan approaches – even when these are correlated to environmental variables. (Resume d'auteur)

The coupling hypothesis: why genome scans may fail to map local adaptation genes.

The mussels Mytilus edulis L. and M. trossulus Gould are found sympatrically in most areas of Newfoundland, with a low frequency of hybrids. To assess the potential for reproductive isolation, we sampled mussels from three sites in an eastern Newfoundland Bay from May–October 1996 to determine if there were differences in the reproductive cycles of the two species and their natural hybrids. In mussels with sheil lengths of 38–42 mm, males and females with mature gametes were dominant in June for M. edulis and hybrids, while M. trossulus showed a lower frequency of individuals with mature gametes. M. trossulus and hybrids spawned over a prolonged period (from late spring to early autumn) compared with most M. edulis individuals that spawned over a period of 2–3 weeks in July. This asynchrony in spawning activity between the two species may partially explain the low frequency of hybrids found in previous studies of these mussel populations. Female and male hybrids between M. edulis and M. trossulus showed normal gonad development, ripening and spawning, providing an opportunity for the introgression of genes between the two species. M. trossulus had a higher reproductive output than M. edulis of similar shell length, while hybrids showed intermediate values of reproductive output. M. trossulus females produced smaller eggs than either M. edulis or hybrids. Differences in reproductive traits may partially explain the maintenance of the mussel hybrid zone in Newfoundland.

/pdf/reproductive-isolation-and-reproductive-output-in-two-3yuqm3fj60.pdf

Reproductive isolation and reproductive output in two sympatric mussel species ( Mytilus edulis, M. trossulus ) and their hybrids from Newfoundland

Recent developments, status, and prospects of molluscan aquaculture on the Pacific coast of South America

Abs tra ctShell -sh ap e variation in th e C h ilean blue m u sselMyt ilu s chi len sis w as exam ined in eight popu la-tions coverin g th e tota lity of its distribu tion ran ge,which repr esen ts ov er 1800 km of la titu din al gradi-en t in the sou thea ste rn Paci¢c . The sh ell ou tlinesh ap es w ere assessed us in g elliptic Fou rier an alysisfollow ed by can on ica l variates an a lysis. Fou riercoeU cien ts show ed a h igh ly sign i¢ca n t m orpholo gi-cal variation be tw een the popu lations stud ied.Ca n on ica lva riates an alysis show ed a visu alassocia-tion of th e First ca n on ica l w ith con vexity of ven traledge an d u mbo sh ap e,w h ile the second axis w as as-sociated w ith sh ell elon gation . P reviously describe dge net ic pa tterns were m argin ally con gru en t w ithou r m orphomet ric pattern , thou gh ge o graph ic dis-ta n ce h ad a stron ge r eAect on m orphol ogy . Sh apech an ge (elon gation ) w as correlated w ith latitu din alclin alvariation .The m orphomet rica lan alysis provedto be an im portan t to ol for ev alu atin g th e com po -ne n ts of shell -sh ape va riation in m u ssels and todocu me n t association pa tterns w ith ge ogr aph ica lan d ecolo gica lva riables. Such pa tterns a re u sefu ltoestablish a w ide ¢eld ofw ork ,in clu d in g sexin g,sto ckrec og n ition , traceab ility stu dies an d prod uc tivem an age me n t in ge ner al.K e y w ord s: in ter-grou p d iscrim in ation , im agea n a lysis, ou tlin es, elliptic Fou rier a n a lysis, ca n on i-cal va riates an alysis, biog eogr aph y, M ytilus chilen-sis,blu e muss elsIntroductionThe C h ilean blue m u ssel Myt ilu s chilensis (H u pe185 4) is w idely distribu ted on h ard subs trates fromth e low er in tertida lzone to depth s o f25 m alon g theC h il ea nco s(Br rþm & Joh 1983). Ir ang e the S E P c i¢c vrs 4 0 1 f l ude ,f rom A ica ( 18 S)to Cape H n56 (La cellott iV et l .6 ) The if-f e rnt iaion pa tte ws c orel ted ith aph -cal d ista n ce, su gges tin g a steppin g-stone m odel ofth e pop u lation stru ctu re. Th is m odel w a s exp ecteddue to th e large dispersalability o flon g-lived plan kto -troph ic la rvae a n d th e pattern o f ocean cu rren tsalon g the C h i le nco s (Toro et .200 4, 0 6) I ad-d ition , a nly sof hell mrphol gy u lnea or -phomet ic v ab l es on three po u ions w nsou ther nC hile ar g how d oupopu lation (P u n ta A ren a s) w as th e m os t d iverge n t(Toro et al.200 4).In th e presen t study w e exam in ed shell m orphol -ogy variation to see if it follow ed th e sa m e pattern ofge net ic m ark ers alon g the 18 00 -k m grad ien t.To da te,m ost m orpholo gica l an alyses of Myti lus sp. shel lsh ave be en ba sed on she ll linea r m orphomet ric

Shell‐shape variation along the latitudinal range of the Chilean blue mussel Mytilus chilensis (Hupe 1854)

The mussel species Mytilus edulis L. and M. trossulus Gould coexist and hybridize throughout a large area that includes the north coast of Maine and Atlantic Canada. Previous studies provided genetic evidence for limited hybridization between the two species for mussels >15 mm. The present study used two genetic markers (ITS, Glu-5′) to examine the genetic composition of early life-history stages by sampling veliger and pediveliger larvae, juveniles ( 15 mm shell length) in Trinity Bay, Newfoundland, during three consecutive years (1995–1997) to determine if differential mortality limits the relative abundance of hybrids. The relative frequency of the two species and the different hybrid genotypes was similar among the larvae, juveniles and small adult mussels. The double hybrid genotype (F1-like) was the rarest genotype observed. There was no evidence for differential mortality during the early life-history stages, and factors limiting production of hybrids appear to operate before the late larval stage. The observed frequency of hybrids is probably due to a combination of pre- and postzygotic reproductive isolating mechanisms operating early in the mussel’s life history. M. trossulus dominated the early life-history stages, possibly due to a higher population density and a greater reproductive output than M. edulis. Differential mortality may explain the observed decrease in frequency of M. trossulus and increase in frequency of M. edulis with increasing shell length. A similar frequency of hybrid mussels from larvae to the size class of 55 mm shell length may indicate a rate of mortality intermediate between the two parental species. The M. edulis–M. trossulus hybrid zone appears to be maintained by reproductive isolating mechanisms limiting the production of hybrids and life-history differences that allow the two species to coexist.

/pdf/genetic-variation-among-life-history-stages-of-mussels-in-a-1jhiu2qpad.pdf

Genetic variation among life-history stages of mussels in a Mytilus edulis-M. trossulus hybrid zone

PCR-based nuclear and mtDNA markers and shell morphology as an approach to study the taxonomic status of the Chilean blue mussel, Mytilus chilensis (Bivalvia)

Jorge E. Toro

Papers

Reproductive isolation and reproductive output in two sympatric mussel species ( Mytilus edulis, M. trossulus ) and their hybrids from Newfoundland

Recent developments, status, and prospects of molluscan aquaculture on the Pacific coast of South America

Shell‐shape variation along the latitudinal range of the Chilean blue mussel Mytilus chilensis (Hupe 1854)

Genetic variation among life-history stages of mussels in a Mytilus edulis-M. trossulus hybrid zone

PCR-based nuclear and mtDNA markers and shell morphology as an approach to study the taxonomic status of the Chilean blue mussel, Mytilus chilensis (Bivalvia)