Estimating sexual selection and sexual isolation effects from mating frequencies

Abstract.— Sexual selection (defined as the change in genotypic or phenotypic frequencies of mated versus total population frequencies) and sexual isolation (defined as the deviation from random mating in mated individuals) show different evolutionary consequences and partially confounded causes. Traditionally, the cross-product estimator has been used to quantify sexual selection, whereas a variety of indexes, such as Yule V , Yule Q, YA , joint I , and others have been used to quantify sexual isolation. Because the two types of estimators use different scales, the effects of both processes cannot be monitored simultaneously. We describe three new related statistics that quantify both sexual selection ( PSS ) and sexual isolation ( PSI ) effects for every mating pair combination in polymorphic traits, as well as measure their combined effects ( PTI = PSI X PSS ). The new statistics have the advantage of providing information on every mating pair combination, quantifying the effects of sexual selection and isolation in the same units, and detecting asymmetry in sexual isolation. The ability of the new statistics to ascertain the biological causes of sexual selection and sexual isolation are investigated under different models involving distinct marginal frequencies, mate propensity, and mate choice coefficients. We also studied the use of classical isolation indexes applied on PSI coefficients, instead of on raw data. The use of the classical indexes applied to PSI coefficients considerably reduces the statistical bias of the estimates, revealing the good estimation properties of the new statistics.     

Reproductive trait divergence and hybrid fertility patterns between chromosomal races of the house mouse in Tunisia: analysis of wild and laboratory-bred males and females

The divergence in reproductive features and hybrid fertility patterns between two chromosomal races (2 n  = 40, 40St, and 2 n  = 22, 22Rb) of the house mouse in Tunisia were re-assessed on a larger sample of wild and laboratory-bred individuals than studied hitherto. Results showed that litter sizes were significantly smaller in 40St than in 22Rb mice, contrary to previous analyses. This suggests that variation in litter size between the two chromosomal races is more likely related to selective and/or environmental factors acting locally than to interracial reproductive trait divergence. However, the significantly reduced litter size of F₁ hybrids compared with parental individuals was confirmed, and further highlighted a sex difference in hybrid infertility, as F₁ females produced fewer litters and of smaller size than males. Histological analyses of F₁ and backcrosses showed a breakdown of spermatogenesis in males and a significantly reduced primordial follicle pool in females. The degree of gametogenic dysfunction was not related to the level of chromosomal heterozygosity per se , but a significant effect of two Rb fusions on follicle number was observed in hybrid females. These results suggest that genetic incompatibilities contribute to primary gametogenic dysfunction in hybrids between the chromosomal races in Tunisia.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 407–416.     

Population divergence in the amphicarpic species Amphicarpaea edgeworthii Benth. (Fabaceae): microsatellite markers and leaf morphology

Comparative analyses of the genetic differentiation in microsatellite markers ( F _ST) and leaf morphology characters ( Q _ST) of Amphicarpaea edgeworthii Benth. were conducted to gain insight into the roles of random processes and natural selection in the population divergence. Simple sequence repeat analyses on 498 individuals of 19 natural populations demonstrate that a significant genetic differentiation occurs among populations (mean F _ST = 0.578), and A. edgeworthii is a highly self-fertilized species (mean selfing rate s  = 0.989). The distribution pattern of genetic diversity in this species shows that central populations possess high genetic diversity (e.g. population WL with H _E = 0.673 and population JG with H _E = 0.663), whereas peripheral ones have a low H _E as in population JD (0.011). The morphological divergence of leaf shape was estimated by the elliptical Fourier analysis on the data from 11 natural and four common garden populations. Leaf morphology analyses indicate the morphological divergence does not show strong correlation with the genetic differentiation ( R  = 0.260, P  = 0.069). By comparing the 95% confidence interval of Q _ST with that of F _ST, Q _ST values for five out of 12 quantitative traits are significantly higher than the average F _ST value over eight microsatellite loci. The comparison of F _ST and Q _ST suggests that two kinds of traits can be driven by different evolutionary forces, and the population divergence in leaf morphology is shaped by local selections.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 505–516.     

Clinal genetic variation and isolation by distance in the European eel Anguilla anguilla (L.)

The genetic variability and structure of the European eel ( Anguilla anguilla L.) in populations throughout Europe was reassessed using 15 allozymic loci, seven of which were polymorphic. Seven sites were sampled on a latitudinal gradient across the natural continental range, extending from southern France to southern Norway. Heterozygosity ( H _e = 0.05) and level of polymorphism (P = 0.43) were comparable to other marine fish. Populations were poorly differentiated ( G _ST = 0.014, F _ST = 0.002), which is not surprising considering the high dispersal capability of the European eel. However, a significant geographical cline was detected at two alleles ( IDH-1 * 100 and GPI-1 * 110 ), and genetic distances ( D _CE) were concordant with geographical coastal distances. Mantel tests, pairwise F _ST's and multidimensional scaling analyses identify three distinct groups: Northern Europe, Western Europe and the Mediterranean Sea. We propose that the clinal genetic structure in the European eel may be due to (1) isolation by distance (as recently detected with microsatellites), (2) temporal reproductive separation, (3) post-larval selective forces, (4) contact between formerly separated groups or (5) some combination thereof.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 509–521     

Karyological studies in Jaborosa (Solanaceae)

Sixteen species of Jaborosa (Solanaceae), including eight endemic to Argentina, were studied karyologically. The numbers n  = 12 and/or 2n  = 24 were found in all species, the majority of the cases being new reports. Mitotic chromosomes were small- to medium-sized, the average length varying from 2.95 to 4.93 µm. All species had one to three chromosome pairs with satellites. The karyotypes, obtained for 13 species, were slightly asymmetrical: A ₁ ranged from 0.228 to 0.483, A ₂ ranged from 0.095 to 0.182, and Paszko's asymmetry index ranged from 0.84 to 3.47. In all species, metacentric chromosomes were the most common, followed by submetacentrics, but subtelocentrics were rare. Morphological similarities and sectional arrangements were not reflected in either a principal components analysis plot or asymmetry index plot, but the species could be singled out by their karyotype formulae and the different karyotype parameters taken. In Jaborosa , a notably diversified genus, exo-morphological evolution has taken place, together with evident chromosome rearrangements, whose disposition is different and not as clear as in related genera.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 467–478.     

Allozyme, mitochondrial-DNA, and morphometrie variability indicate cryptic species of anchovy (Engraulis encrasicolus)

Previous surveys of population structure in the Atlantic-Mediterranean anchovy Engraulis encrasicolus L. have reported heterogeneity in morphology, allozyme frequencies, and mitochondrial DNA haplotype frequencies at a regional scale. In particular, two stocks of anchovy have been detected in the Adriatic Sea. In this paper, the available data is reviewed with the aim to relate genetic variation to geography at the widest possible geographical scale, for investigating the evolutionary mechanisms underlying stock structure in anchovy. Correspondence analysis of allozyme frequencies (24 samples, three polymorphic loci) compiled from the literature indicates three distinct entities in the Mediterranean Sea. Open-sea or oceanic anchovy populations are genetically different from inshore-water populations within a region (Nei's ^ G _ST = 0.035–0.067), while broadscale geographical variation is weak for each of these two habitat-specific forms (^ G _ST = 0.005–0.006). Mitochondrial-DNA haplotype frequencies support the distinction between an inshore form and an oceanic form (^ G _ST = 0.067–0.107), with virtually no genetic differences among oceanic populations across the Gulf of Biscay, the western Mediterranean and the Ionian Sea (^ G _ST = −0.001). If natural selection on marker loci is unimportant, these results indicate the occurrence of two parapatric, genetically distinct, habitat-specific forms that are widely distributed throughout the Mediterranean Sea. Persistent allele and haplotype-frequency differences between these forms indicate reproductive isolation and the presence of an E. encrasicolus species complex in the Mediterranean. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society 75 : 261–269.     

Maintenance of species boundaries despite rampant hybridization between three species of reef fishes (Hexagrammidae): implications for the role of selection

Hybridization and introgression are antagonistic to the process of speciation. If hybrids are viable and backcross, introgression will slow or prevent the evolution of reproductive isolation between populations. If species hybridize upon secondary contact, introgression will ultimately erode species boundaries. If hybridization is rampant and gene flow is high, the proportion of hybrids will approach values expected with random mating, and introgression will overcome species boundaries, homogenizing populations. Alternatively, if species are genetically distinct, the proportion of hybrids would be significantly less than expected with random mating, gene flow would be interrupted by selection against hybrids, and inviability or sterility of F ₁ hybrids or backcrosses would be expected. Here, we investigate a system with characteristics expected by both of these opposing scenarios. Hybridization occurs between three species of reef fishes in the genus Hexagrammos at unexpected high frequencies in a zone of distributional overlap. Backcrossed individuals are detected, indicating F ₁ hybrids are viable and capable of reproducing. Yet, these species are genetically distinct at multiple loci. To study this apparent paradox, we estimate the relative proportions of hybrids, patterns of symmetry, inviability, and cytonuclear disequilibria using one mitochondrial and two nuclear markers. We invoke selection against hybrids, at various life history stages, in the maintenance of species boundaries in this system.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 135–147.     

Alkane composition diversity among populations of dwarf forms of Juniperus communis L.: comparison between western Europe and northern American populations

The cuticular wax composition of leaves has been analysed in three western European populations (Corsica, central Pyrenees, northern Alps) of Juniperus communis var. saxatilis Pall. (=  J. nana Willd., nom illeg.) and in one population of J. communis L. var. depressa Pursh. from North America (Sierra Nevada). Gas chromatography shows the presence of 13 alkanes in all samples ranging from C₂₃ to C₃₅ with important intraspecific polymorphism in alkane content. The dominant alkanes range from C₃₃ to C₃₅. Alkanes C₂₁ and C₂₂ were found only in Corsica and Sierra Nevada populations. Canonical discriminant analysis separated the J. communis L. var. depressa Pursh. of the population of Sierra Nevada from other populations of J. communis var. saxatilis Pall. on the basis of their higher C₃₁ content and the constant presence of C₂₁ and C₂₂ alkanes. J. communis var. saxatilis Pall. populations from the Pyrenees are close to northern Alps populations characterized by high concentrations of C₃₃, C₃₄ and C₃₅ alkanes. This paper confirms the existence of Juniperus var. saxatilis Pall. in the Pyrenees (France).  © The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 140 , 165–168.     

Phylogeography and species limits in the Gymnodactylus darwinii complex (Gekkonidae, Squamata): genetic structure coincides with river systems in the Brazilian Atlantic Forest

Phylogenetic analyses based on mtDNA cytochrome  b were performed in 42 lizards of the Gymnodactylus darwinii complex from three regions within Brazil's Atlantic Forest. Mainland regions and continental shelf islands in the south-eastern range and mainland areas from the north-east were sampled. The criteria of maximum parsimony (MP), maximum likelihood (ML) and Bayesian methods were explored, with the robustness for nodes assessed by bootstrapping (MP and ML) and posterior probabilities (Bayesian searches). By all methods, three distinctive phylogroups were recovered: a south-eastern clade (SE) and two clades from northern regions (NE₁ and NE₂). The pattern of genetic structure of the major clades coincided with the presence of river systems in the Atlantic Forest, and based on corrected genetic distances between those clades, divergence times were tentatively estimated using mtDNA rates calibrated for squamate reptiles. The putative role of Atlantic Forest rivers in generating differentiation is discussed. We present a hypothesis of species limits for G. darwinii , based on concordant lines of evidence including cytogenetic and mtDNA analyses. Two chromosome races (cytotype A, 2n = 38; and cytotype B, 2n = 40) had distributions concordant with clades SE and NE₁ + NE₂, respectively. These races are interpreted to be full species on the basis of a number of empirical criteria.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 13–26.     

Three parameters comprehensively describe the temperature response of respiratory oxygen reduction

Using an exponential model that relies on Arrhenius kinetics, we explored Type I, Type II and dynamic (e.g. declining Q ₁₀ with increasing temperature) responses of respiration to temperature. Our Arrhenius model provides three parameters: R _REF (the base of the exponential model, nmol g⁻¹ s⁻¹), E ₀ (the overall activation energy of oxygen reduction that dominates its temperature sensitivity, kJ mol⁻¹) and δ (that describes dynamic responses of E ₀ to measurement temperature, 10³ K²). Two parameters, E ₀ and δ , are tightly linked. Increases in overall activation energy at a reference temperature were inversely related to changes in δ . At an E ₀ of ca. 45 kJ mol⁻¹, δ approached zero, and respiratory temperature response was strictly Arrhenius-like. Physiologically, these observations suggest that as contributions of AOX to combined oxygen reduction increase, E ₀( REF ) decreases because of different temperature sensitivities for V _max, and δ increases because of different temperature sensitivities for K _1/2 of AOX and COX. The balance between COX and AOX activity helps regulate plant metabolism by adjusting the demand for ATP to that for reducing power and carbon skeleton intermediates. Our approach enables determination of respiratory capacity in vivo and opens a path to development of process-based models of plant respiration.     

Hybrids between Chorthippus brunneus and C. jacobsi (Orthoptera: Acrididae) do not show endogenous postzygotic isolation

Studies of prezygotic and postzygotic isolation in Drosophila have shown in general that species in sympatry tend to evolve prezygotic barriers earlier than do species in allopatry. However, postzygotic barriers tend to evolve at the same evolutionary rate in both sympatric and allopatric species. In contrast to these observations, the grasshoppers Chorthippus parallelus parallelus and C. p. erythropus show complete hybrid male sterility but only limited prezygotic isolation after an estimated 0.5 millions years of divergence. Like their congeners, C. brunneus and C. jacobsi form a hybrid zone where their ranges meet in northern Spain. However, the hybrid zone is mosaic and bimodal and, in contrast to the high levels of postzygotic isolation between C. parallelus subspecies, these two species showed no significant reduction in hybrid fitness in F₁ or backcross generations relative to the parental generations. The level of prezygotic isolation in laboratory tests was comparable to that between C. parallelus subspecies. These results suggest that endogenous postzygotic isolation does not play an important role in the reproductive isolation between C. brunneus and C. jacobsi , or in determining the structure of the hybrid zone. Exogenous postzygotic isolation may be present and should be tested in future studies.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 195–203.     

Hybrid queen butterflies from the cross Danaus chrysippus (L.) × D. gilippus (Cramer):confirmation of species status for the parents and further support for Haldane's Rule

A cross between queen butterflies of the Palaeotropical species Danaus chrysippus and the Neotropical D. gilippus was achieved with difficulty in both directions. Only one progeny ( N  = 70) was reared comprising sterile males and inviable females in a precisely 1 : 1 ratio. Both prezygotic and postzygotic barriers to gene flow are strong. The result supports Haldane's Rule, to which we propose a minor amendment. The F₁ hybrids were intermediate for background colour between the brown (genotype BB ) of gilippus and orange (genotype bb ) of chrysippus . Most F₁ pattern characters were also intermediate. In polymorphic chrysippus populations, because Bb heterozygotes are brown, or nearly so, we suggest the B allele may have evolved towards dominance in sympatry. Hybrid males show positive heterosis for body size. The close similarity of male genitalia between the allopatric, genetically distant species chrysippus  and gilippus , compared to their divergence between gilippus and its largely sympatric sister species eresimus , suggest that reinforcement of sexual isolation or reproductive character displacement have evolved in sympatry.  © 2002 The Linnean Societyof London, Biological Journal of the Linnean Society , 2002, 76 , 535–544.     

Postzygotic isolation between the two European subspecies of the house mouse: estimates from fertility patterns in wild and laboratory-bred hybrids

We assessed the fertility (reproductive success, litter size, testis weight, spermatocyte-to-spermatid ratio) of F₁s and backcrosses between different wild-derived outbred and inbred strains of two mouse subspecies, Mus musculus domesticus and M. m. musculus . A significant proportion of the F₁ females between the outbred crosses did not reproduce, suggesting that female infertility was present. As the spermatocyte-to-spermatid ratio was correlated with testis weight, the latter was used to attribute a sterile vs. fertile phenotype to all males. Segregation proportions in the backcrosses of F₁ females yielded 11 (inbred) to 17% (outbred) sterile males, suggesting the contribution of two to three major genetic factors to hybrid male sterility. Only one direction of cross between the inbred strains produced sterile F₁ males, indicating that one factor was borne by the musculus X-chromosome. No such differences were observed between reciprocal crosses in the outbred strains. The involvement of the X chromosome in male sterility thus could not be assessed, but its contribution appears likely given the limited introgression of X-linked markers through the hybrid zone between the subspecies. However, we observed no sterile phenotypes in wild males from the hybrid zone, although testis weight tended to decrease in the centre of the transect.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 379–393.     

Reduction of chromosome number in Eleocharis subarticulata (Cyperaceae) by multiple translocations

Eleocharis subarticulata is recorded as the third species of Cyperaceae with a reduced chromosome number ( n  = 3), following reports on Rhynchospora tenuis ( n  = 2) and Fimbristylis umbellaris ( n  = 3). For Eleocharis, the numbers recorded to date vary from 2 n  = 10 to 2 n  = c. 196, with x  = 5 as the possible basic number. The karyotype of E. subarticulata was studied using conventional staining (mitosis and meiosis), C-CMA₃/DAPI banding, and FISH with 45S rDNA and telomere probes. The chromosomes showed no primary constrictions, as expected in the holocentric chromosomes of Cyperaceae. The meiotic behaviour was abnormal, with a single multivalent ring of six chromosomes at metaphase I, resulting from multiple translocations. At anaphase I six chromatids migrated to each pole, evidencing the inverted meiosis, and these groups were also visible at metaphase II. The C-CMA₃/DAPI banding technique showed only four terminal GC-rich blocks. FISH with 45S rDNA probes revealed four terminal signals, probably associated with GC-rich blocks. The telomeric probe located terminal signals in all the chromosomes, besides a hybridization site in the middle of the large pair. The occurrence of ectopic telomeric sites has not been described previously for plants with holokinetic karyotypes and with reduced chromosome numbers. These data reinforce the hypothesis of the reduction in chromosome number by multiple translocations.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 457–464.     

Sex chromosome variability outlines the pathway to the chromosomal evolution in Microtus thomasi (Rodentia, Arvicolinae)

The underground vole Microtus thomasi , a Balkan endemic, displays remarkable variability in sex chromosome size and morphology. In the present study, we demonstrate this variability in two of its chromosomal races with 2 n  = 44 (i.e. 'thomasi' and 'atticus') with the use of C-banding on a sample of 189 individuals from 50 localities of Greece. In 'thomasi', five different, acrocentric X chromosome variants (X₀–X₄) are described, which differ significantly in size, due to heterochromatin addition. Also, three Y chromosome variants are described (Y₀–Y₂), ranging in size from very small (Y₀) to large (Y₂). The 'atticus' race displays three subtelocentric variants of the X chromosome (X_st0–X_st2), which differ in arm length ratio and heterochromatin content. In Peloponnesus, males of this race exhibit Y₀ and Y₁, whereas, in Attiki (south-east Sterea Ellada), males carry the small metacentric, Y_m. Overall, there is a trend towards sex chromosome size increase in a south to north direction. We propose that the last glaciation must have restricted M. thomasi to a refugium in southern Peloponnesus. During post-glacial colonization, limited northward expansion of its distribution area must have been accompanied by consecutive heterochromatin addition, which is proven today by comparatively larger sex chromosomes in the northern populations of 'thomasi' and 'atticus' in Greece than in their southern populations.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 685–695.     

Stomatal response to humidity: implications for transpiration

Abstract. Transpiration rates from apple leaves are analysed in terms of the ratio of latent heat flux (λ E ) to leaf net radiation ( Q ₁) and the climatological resistance ( r_i ). Increases in stomatal resistance with increasing leaf to air vapour pressure gradient ( D ), described by an empirical model, are incorporated in the analysis. This humidity effect causes the proportion of energy dissipated as latent heat to fall as Q ₁ increases, so that leaf transpiration rates in high energy environments are likely to be similar to those in lower energy environments. Boundary layer resistance ( r _a) exerts an increasingly important effect on transpiration rates as Q ₁ increases. At constant Q ₁ stomatal closure in response to increasing D results in very small changes in leaf temperature ( T ₁) across a wide range of ambient vapour pressure deficits (δ e ); r _a is then the major factor determining T ₁. The implications of these results are discussed.     

Morphological and geographic variation of the cycad Dioon edule Lindl. (Zamiaceae): ecological and evolutionary implications

The relationship in geographical distribution and morphological variation of leaflet width and length (diagnostic trait), between and within populations of Dioon edule Lindl., has been investigated throughout its known range in eastern Mexico (from the states of Nuevo León to Veracruz, north to south, respectively). A total of 1832 leaflets were measured for width and length from 154 plants distributed amongst five populations using four leaflet replicas from each of three leaves per plant. For leaflet width and length the variation among populations indicated significant stat-istical differences ( F _4,147 = 125.83; P  < 0.0001; R ² = 92.17% and F _4,147 = 9.04; P  < 0.001; R ² = 26.8%), respectively. With respect to leaflet width, the multiple range test showed three groups with a north to south distributional relationship along the range of the species. The correlation coefficient among paired populations, respect to geographical distance and the absolute value of the mean difference of leaflet width in each population, was positive, and different from zero ( r  = 0.82; P  = 0.013). A great variation of important ecological and evolutionary parameters was shown.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 465–470.     

Selectivity of diamond, square and hexagonal mesh codends for Atlantic horse mackerel Trachurus trachurus, European hake Merluccius merluccius, and greater forkbeard Phycis blennoides in the eastern Mediterranean

Knowledge on selectivity is considered essential for an adequate management of the trawl fishery. This paper compares the selectivity of conventionally used codends of 44 mm diamond mesh, 40 mm square, and hexagonal mesh for Atlantic horse mackerel, European hake and greater forkbeard in the eastern Mediterranean. Data were collected using the covered codend method and analyzed using the logistic equation with the maximum likelihood method. Mean selection curves were analyzed and compared using the between-haul variations model. The mean L ₅₀ v alues of diamond, square and hexagonal mesh codends are 14.7, 15.9 and 17.1 cm total length (TL) for horse mackerel, 10.4, 14.4 and 11.0 cm TL for hake and 12.2, 15.8 and 12.7 cm TL for greater forkbeard, respectively. For horse mackerel, the differences among the codends are statistically significant (P   <   0.05); however, the L ₅₀ values for all three meshes are higher than the minimum landing size (13 cm TL). For hake and greater forkbeard, the L ₅₀ value for the square mesh codend is significantly different from the values for diamond and hexagonal meshes (P   <   0.01), whereas there is no significant difference between diamond and hexagonal meshes (P   >   0.05). Regardless of the mesh shape, L ₅₀ values were substantially lower than the minimum landing size or size at first maturity for hake and greater forkbeard. To enable more effective solutions, research on species-selective trawls is required for the Mediterranean demersal trawl fishery.     

Large variations in the ratio of effective breeding and census population sizes between two species of pond-breeding anurans

The viability of wild populations is frequently assessed by monitoring adult census sizes ( N _c). This approach is particularly useful for pond-breeding amphibians, because assemblages during the breeding season are relatively easy to detect and count. However, it is the genetic effective population size ( N _e) or surrogates such as effective breeding population size ( N _b) that are of primary importance for long-term viability. Although N _c estimates of one anuran amphibian ( Bufo bufo ) in Britain were much larger than those of another ( Rana temporaria ) at the same sites, the ratios of N _b to N _c were much smaller in B. bufo than in R. temporaria. These differences were sufficiently great as to reverse the effective size order at one site, such that N _b for R. temporaria was larger than that for B. bufo. Differences in adult sex ratios at breeding sites probably contributed to lower N _b values in B. bufo populations compared with those of R. temporaria . The relationship of N _b to N _c can therefore vary dramatically even between similar species, to the extent that just monitoring N _c can give misleading impressions of relative effective breeding sizes and thus of population viability. It will be increasingly important to estimate N _e or N _b in wildlife populations for assessment of conservation priorities.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 365–372.