▪ Abstract Most models of optimal progeny size assume that there is a trade-off between progeny size and number, and that progeny fitness increases with increasing investment per young. We find that both assumptions are supported by empirical studies but that the trade-off is less apparent when organisms are iteroparous, use adult-acquired resources for reproduction, or provide parental care. We then review patterns of variation in progeny size among species, among populations within species, among individuals within populations, and among progeny produced by a single female. We argue that much of the variation in progeny size among species, and among populations within species, is likely due to variation in natural selection. However, few studies have manipulated progeny environments and demonstrated that the relationship between progeny size and fitness actually differs among environments, and fewer still have demonstrated why selection favors different sized progeny in different environments. We argue ...

Evolutionary ecology of progeny size in arthropods.

Global warming and increased atmospheric co2 are causing the oceans to warm, decrease in pH and become hypercapnic. These stressors have deleterious impacts on marine inver - tebrates. Increasing temperature has a pervasive stimulatory effect on metabolism until lethal levels are reached, whereas hypercapnia has a narcotic effect. ocean acidification is a major threat to cal - cifying larvae because it decreases availability of the carbonate ions required for skeletogenesis and also exerts a direct pH effect on physiology. Marine invertebrate propagules live in a multistressor world and climate change stressors are adding to the mix. ocean pH, pco2 and caco3 covary and will change simultaneously with temperature, challenging our ability to predict future outcomes for marine biota. To address questions of future vulnerabilities, data on the thermo- and pH/ pco2 tolerance of fertilization and development in marine invertebrates are reviewed in the context of the change in the oceans that are forecast to occur over the next 100-200 years. Gametes and fertilization in many invertebrates exhibit a broad tolerance to warming and acidification beyond stressor values projected for 2100. Available data show that all development stages are highly sensitive to warming. larvae may be particularly sensitive to acidification/hypercapnia. Embryos that develop through the bottleneck of mortality due to warming may succumb as larvae to acidification. Early juveniles may be vulnerable to skeletal dissolution, although warming may diminish the negative impact of acidifi - cation on calcification. The effects of climate change stressors and their interaction differ among life history stages and species. Multistressor experiments show that if thermal thresholds are breached, embryos may not reach the calcifying stage. If the bottleneck for species persistence is embryonic thermotolerance, then the question of compromised calicification due to acidification may not be relevant. our limited knowledge of the interactive effects of climate change stressors is a major knowledge gap. Although climate change is deleterious for development in a broad range of marine invertebrates, some species and regional faunas will be more resilient than others. This has implica- tions for persistence, faunal shifts, species invasions and community function in a changing ocean.

Impact of ocean warming and ocean acidication on marine invertebrate life history stages: Vulnerabilities and potential for persistence in a changing ocean

Theoretical studies of speciation have been dominated by numerical simulations aiming to demonstrate that speciation in a certain scenario may occur. What is needed now is a shift in focus to identifying more general rules and patterns in the dynamics of speciation. The crucial step in achieving this goal is the development of simple and general dynamical models that can be studied not only numerically but analytically as well. I review some of the existing analytical results on speciation. I first show why the classical theories of speciation by peak shifts across adaptive valleys driven by random genetic drift run into trouble (and into what kind of trouble). Then I describe the Bateson-Dobzhansky-Muller (BDM) model of speciation that does not require overcoming selection. I describe exactly how the probability of speciation, the average waiting time to speciation, and the average duration of speciation depend on the mutation and migration rates, population size, and selection for local adaptation. The BDM model postulates a rather specific genetic architecture of reproductive isolation. I then show exactly why the genetic architecture required by the BDM model should be common in general. Next I consider the multilocus generalizations of the BDM model again concentrating on the qualitative characteristics of speciation such as the average waiting time to speciation and the average duration of speciation. Finally, I consider two models of sympatric speciation in which the conditions for sympatric speciation were found analytically. A number of important conclusions have emerged from analytical studies. Unless the population size is small and the adaptive valley is shallow, the waiting time to a stochastic transition between the adaptive peaks is extremely long. However, if transition does happen, it is very quick. Speciation can occur by mutation and random drift alone with no contribution from selection as different populations accumulate incompatible genes. The importance of mutations and drift in speciation is augmented by the general structure of adaptive landscapes. Speciation can be understood as the divergence along nearly neutral networks and holey adaptive landscapes (driven by mutation, drift, and selection for adaptation to a local biotic and/or abiotic environment) accompanied by the accumulation of reproductive isolation as a by-product. The waiting time to speciation driven by mutation and drift is typically very long. Selection for local adaptation (either acting directly on the loci underlying reproductive isolation via their pleiotropic effects or acting indirectly via establishing a genetic barrier to gene flow) can significantly decrease the waiting time to speciation. In the parapatric case the average actual duration of speciation is much shorter than the average waiting time to speciation. Speciation is expected to be triggered by changes in the environment. Once genetic changes underlying speciation start, they go to completion very rapidly. Sympatric speciation is possible if disruptive selection and/or assortativeness in mating are strong enough. Sympatric speciation is promoted if costs of being choosy are small (or absent) and if linkage between the loci experiencing disruptive selection and those controlling assortative mating is strong.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.0014-3820.2003.tb00233.x

Perspective: models of speciation: what have we learned in 40 years?

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

Marine organisms exhibit great variation in reproductive modes, larval types, and other life-history traits that may have major evolutionary consequences. We measured local and regional patterns of genetic variation in corals along Australia's Great Barrier Reef to determine the relative contributions of sexual and asexual reproduction to recruitment and to infer levels of gene flow both locally (among adjacent sites, < 5 km apart) and regionally (among reefs separated by 500-1,200 km). We selected five common brooding species (Acropora cuneata, A. palifera, Pocillopora damicornis, Seriatopora hystrix, and Stylophora pistillata) and four broadcast spawners (Acropora hyacinthus, A. cytherea, A. millepora, and A. valida), which encompassed a wide range of larval types and potential dispersal capabilities. We found substantial genotypic diversity at local scales in six of the nine species (four brooders, two spawners). For these six, each local population displayed approximately the levels of multilocus genotypic diversity (Go) expected for outcrossed sexual reproduction (mean values of Go:Ge ranged from 0.85 to 1.02), although consistent single-locus heterozygous deficits indicate that inbreeding occurs at the scale of whole reefs. The remaining three species, the brooder S. hystrix and the spawners A. valida and A. millepora displayed significantly less multilocus genotypic diversity (Go) than was expected for outcrossed sexual reproduction (Ge) within each of several sites. Acropora valida and A. millepora showed evidence of extensive localized asexual replication: (1) a small number of multilocus (clonal) genotypes were numerically dominant within some sites (Go:Ge values were as low as 0.17 and 0.20): (2) single-locus genotype frequencies were characterized by both excesses and deficits of heterozygotes (cf. Hardy-Weinberg expectations), and (3) significant linkage disequilibria occurred. For the brooding S. hystrix Go:Ge values were also low within each of four sites (x = 0.48). However, this result most likely reflects the highly restricted dispersal of gametes or larvae, because levels of genetic variation among sites within reefs were extremely high (FSR = 0.28). For all species, we detected considerable genetic subdivision among sites within each reef (high FSR-values), and we infer that larval dispersal is surprisingly limited (i.e., Nem among sites ranging from 0.6 to 3.3 migrants per generation), even in species that have relatively long planktonic durations. Nevertheless, our estimates of allelic variation among reefs (FRT) also imply that for all four broadcast spawning species and three of the brooders, larval dispersal is sufficient to maintain moderate to high levels of gene flow along the entire Great Barrier Reef (i.e., Nem among reefs ranged from 5 to 31). In contrast, widespread populations of S. hystrix and S. pistilata (the two remaining brooders) are relatively weakly connected (Nem among reefs was 1.4 and 2.5, respectively). We conclude that most recruitment by corals is very local, particularly in brooders, but that enough propagules are widely dispersed to ensure that both broadcast spawning and brooding species form vast effectively panmictic populations on the Great Barrier Reef.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.0014-3820.2000.tb00704.x

Genotypic diversity and gene flow in brooding and spawning corals along the Great Barrier Reef, Australia.

at least two types of block may be involved: a fast electriRecent recognition of sperm limitation effects, and quancal block occurring within seconds of sperm contact and tification of resultant variation in fertilization success, has a slower cortical reaction (Schuel 1984). However, in the had important consequences for the understanding of the Vogel et al. model, polyspermy blocks are implicitly ecology and life history of marine organisms that repro‘‘perfect’’ in that, once an initial sperm fertilizes an egg, duce by free spawning (reviewed in Levitan 1995; Levitan there is (instantaneously) no possibility whatsoever that and Petersen 1995). Central to this developing theory is other sperm can also fertilize the egg. In reality, there will the idea that the likelihood of fertilization is a function be a finite time period between the initial fertilization of ambient sperm concentration. Vogel et al. (1982) proand polyspermy block activation while cellular changes duced a mathematical model of this relationship, based necessary to prevent further fertilizations take place. Duron a model of bimolecular kinetics and a random colliing this time, additional fertilizations (hence polyspermy) sion of gametes. This model is the basis of several analymight occur. At least one recent study (Brawley 1992) ses of individual and population fertilization success of found that up to 7% of eggs were polyspermic in a natufree-spawning invertebrates (e.g., Denny 1988; Denny ral population of free-spawning (fucoid) algae. A more and Shibata 1989; Denny et al. 1992; Babcock et al. 1994; realistic model of fertilization kinetics would take into Levitan and Young 1995; Morris 1994), reproductive account the finite time delay in the activation of polystrategies in hermaphroditic fish (Petersen 1991), and gaspermy blocks and be able to predict the likelihood of mete provisioning in invertebrates (Levitan 1993, 1996a, polyspermy. 1996b; Podolsky and Strathmann 1996). The Vogel et al. A more complete model of fertilization kinetics might model, however, examines only the consequences of also address one concern of Podolsky and Strathmann sperm limitation and does not consider the possibility (1996) regarding Levitan’s (1993, 1996b) incorporation that contact with more than one sperm may lead to polyof sperm limitation effects to account for intermediate spermy. egg sizes of at least free-spawning marine invertebrates. The Vogel et al. model assumes that all eggs that are Using the Vogel et al. model, Levitan (1993) suggested contacted and fertilized by at least one sperm develop that, because in sperm-limited conditions larger eggs into normal embryos when, in fact, we would ordinarily provide larger targets for sperm (and increase the rate of expect that fertilization by two or more sperm will result sperm-egg collisions), they should be selected for, counin polyspermy and either mortality or abnormal larval terbalancing other forces that favor small eggs. Podolsky * Present address: South Australian Research and Development Institute, South and Strathmann (1996) reasoned that, if eggs were sperm Australian Aquatic Sciences Centre, P.O. Box 120, West Beach, South Australia limited, why would they not have evolved to become bet5022, Australia; E-mail: Styan.craig@wpo.pi.sa.gov.au. ter targets in a manner that does not require an increase Am. Nat. 1998. Vol. 152, pp. 290–297.  1998 by The University of Chicago.

https://www.jstor.org/stable/10.1086/286168

Polyspermy, Egg Size, and the Fertilization Kinetics of Free‐Spawning Marine Invertebrates

For free‐spawning organisms that release gametes into the sea, sperm limitation (too few sperm to fertilize all eggs) is a major factor limiting reproductive success. Given such circumstances, the presence of several mechanisms to prevent polyspermy (too many sperm) may seem paradoxical; however, a growing body of data suggests that natural fertilization levels, though variable, can routinely be high. Under such conditions, polyspermy is much more likely. The tension between sperm limitation and polyspermy represents sexual conflict because males, in competing to fertilize as many eggs as possible, can impose lethal costs on eggs if multiple sperm gain entry. Here we present data for a marine invertebrate indicating high levels of polyspermy under sperm‐limited conditions. When the sea urchin Evechinus chloroticus was induced to spawn in situ, mean rates of polyspermy were 
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$$17.3\% \pm 3.4\% $$
\end{document} , and polyspermy was recorded at rates as high as 62.7%. Polyspermy was nearly always present, even when fertilization rates were <50%, confirming predictions that it should be present under sperm‐limited conditions. Both sperm limitation and polyspermy imposed substantial reproductive costs, and we conclude that both sexual conflict related to polyspermy and sperm limitation have been simultaneous strong selective forces shaping the evolution of reproductive traits in the sea.

Sexual conflict and polyspermy under sperm-limited conditions: in situ evidence from field simulations with the free-spawning marine echinoid Evechinus chloroticus (vol 160, pg 485, 2002)

In situ and in vitro observations indicate that brooding colonial ascidians commonly display limited larval dispersal, whilst the larvae of most solitary species are assumed to be widely dispersed. We used allozyme data to determine the population genetic consequences of reproduction and dispersal in a broadcast-spawning solitary ascidian and two brooding colonial species along the central and southern coast of New South Wales, Australia. We surveyed genetic variation at 2 to 9 variable loci for samples collected from 6 to 8 local populations of each of the stalked solitary species Pyura gibbosa gibbosa Heller, 1878; the social Stolonica australis Michaelsen, 1927 and the compound Botrylloides magnicoecum Hartmeyer, 1912. Samples from each local population displayed levels and patterns of genotypic diversity that were consistent with expectations for sexually-derived recruitment of both solitary zooids and separate colonies. However, we found clear differences in the structure of the populations of solitary and colonial species. Genotype frequencies within all nine samples of P. gibbosa gibbosa conformed to expectations for random mating (i.e. Hardy–Weinberg equilibria). Moreover, allele frequencies showed little variation among samples [mean standardised genetic variance (FST) =0.002], which implies that local populations are strongly connected by larval dispersal. We estimate (via Wright's “island model”) that gene flow (Nem) within this set of local populations is 125 effective migrants per generation, which is very similar to estimates obtained for other broadcast-spawning taxa in this region. In contrast, genotype frequencies within samples of both colonial species were characterised by large and statistically significant deficits of heterozygotes, consistent with expectations for highly limited dispersal of larvae or sperm. Moreover, local populations were highly differentiated (FST=0.201 and 0.202 for S. australis and B. magnicoecum, respectively) and Nem was estimated to be ∼1.0 in each case. These values of FST and subsequent estimates of Nem lie within the range of values reported for other New South Wales taxa with direct larval development, and imply that local populations are effectively closed to immigration.

Genetic evidence for contrasting patterns of dispersal in solitary and colonial ascidians

For free‐spawning organisms that release gametes into the sea, sperm limitation (too few sperm to fertilize all eggs) is a major factor limiting reproductive success. Given such circumstances, the presence of several mechanisms to prevent polyspermy (too many sperm) may seem paradoxical; however, a growing body of data suggests that natural fertilization levels, though variable, can routinely be high. Under such conditions, polyspermy is much more likely. The tension between sperm limitation and polyspermy represents sexual conflict because males, in competing to fertilize as many eggs as possible, can impose lethal costs on eggs if multiple sperm gain entry. Here we present data for a marine invertebrate indicating high levels of polyspermy under sperm‐limited conditions. When the sea urchin Evechinus chloroticus was induced to spawn in situ, mean rates of polyspermy were \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} ...

https://www.jstor.org/stable/10.1086/342075

Sexual conflict and polyspermy under sperm-limited conditions: in situ evidence from field simulations with the free-spawning marine echinoid Evechinus chloroticus.

Fertilisation of eggs of free-spawning marine invertebrates depends on factors affecting sperm concentration in the field and also on gamete characteristics such as egg size. In the free-spawning intertidal ascidian Pyura stolonifera mean egg size increased with maternal size in 2 separate populations. The largest ascidian produced eggs that were, on average, 50% greater in volume than the eggs produced by the smallest individual studied. There was no evidence to suggest that egg density varied with adult size and egg dry organic weight increased with maternal size. The fertilisation kinetics of this species were strongly affected by the variation in egg size, with the eggs of large individuals requiring much less concentrated sperm to achieve maximal levels of fertilisation success than the eggs of small individuals. We suggest that variation in egg size between individuals of different sizes and ages may be an important factor in determining fertilisation success for ascidians of this species.

/pdf/intraspecific-co-variation-between-egg-and-body-size-affects-z4lpoq90w3.pdf

Craig A. Styan

Papers

Polyspermy, Egg Size, and the Fertilization Kinetics of Free‐Spawning Marine Invertebrates

Sexual conflict and polyspermy under sperm-limited conditions: in situ evidence from field simulations with the free-spawning marine echinoid Evechinus chloroticus (vol 160, pg 485, 2002)

Genetic evidence for contrasting patterns of dispersal in solitary and colonial ascidians

Sexual conflict and polyspermy under sperm-limited conditions: in situ evidence from field simulations with the free-spawning marine echinoid Evechinus chloroticus.

Intraspecific co-variation between egg and body size affects fertilisation kinetics of free-spawning marine invertebrates