The Particular Maternal Effect of Propagule Size, Especially Egg Size: Patterns, Models, Quality of Evidence and Interpretations

SYNOPSIS. Propagule size is perhaps the most widely recognizedand studied maternal effect in ecology, yet its evolution isnot well-understood. The large body of extant optimality theorytreats parental investment solely as an ecological problem,largely from the perspective of progeny. This approach has hadlimited success explaining the ubiquitous variation in propagulesize within and among natural populations at most temporal andspatial scales. This problem aside, an unassailable gap in propagulesize theory is that it pays little heed to the fact that offspringsize is a joint phenotype of two individuals- the offspringand its mother. Hence, the ecology of mothers is decidedly asimportant in shaping the evolution of propagule size phenotypes.There are two reasons to suspect that this gap may account forthe lack of success of optimality theory to explain variationin nature. The first is that optimality models of propagulesize make no allowance for, nor can they explain, widespread,multivariate correlations between maternal characters and clutchparameters, namely the positive phenotypic covariances of maternalage, size, fecundity, and per-propagule investment found inmany organisms. If per-propagule investment is optimized byselection based on the expectation of offspring fitness, thenwhy should that phenotype be a function of maternal age or sizewhen the ecological circumstances of progeny are not changingas a function of maternal age or size? The second gap in currenttheory is that, like all optimization theory, it is patentlynon-genetic in that it is assumed that the phenotypes optimizedare evolutionarily accessible. Recent maternal effects theoryindicates that traits subject to maternal influence behave inunanticipated ways. Specifically, there may be time lags inresponse to selection, and hence, selection away from the optimumphenotype. This paper explores a suite of issues pertainingto the evolution of propagule size from the broader perspectiveof propagule size as a maternal effect (PSME) with a goal ofwidening the lens through which propagule size is viewed byevolutionary ecologists. Two themes are developed. First, Isuggest that, to understand egg size variance and its implicationsfor both maternal and offspring fitness, it is necessary toconsider explicitly the ecological context in which a motheris producing eggs, not just that into which offspring will enter.I argue that some of the variables that have only been incorporatedin pairwise fashion (or not at all) into studies of propagulesize might account for the lack of agreement about how thisimportant life history feature evolves. Further, I suggest thatfailure to consider other sources of selection on maternal phenotypes,driven by a narrow adaptationist view that has historicallybeen taken of PSMEs, has obfuscated many interesting questionssurrounding their coevolution with maternal characters. Thus,the second theme is that it is necessary to consider other explanationsfor why prop-agule size varies apart from those pertaining tooffspring fitness per si. Based on a detailed review of theempirical literature, I conclude that the concept of an optimalpropagule size is not only an insufficient construct to explainthe evolution of propagule size, but that continued relianceon an optimization approach is likely to stifle developmentof more realistic and predictive theory for the evolution ofthis key life history trait. Novel theory should incorporaterealities from physiology, development and genetics and shouldaccommodate the dynamic nature of the selective environmentsin which propagule size evolves, all of which have been shownby empiricists to play a role in determining propagule sizephenotypes. A key feature of this theory should be the explicittreatment of propagule size as a maternal effect.     

BIOLOGY AND POPULATION DYNAMICS OF A CREVICE-DWELLING LANDSNAIL, CRISTATARIA GENEZARETHANA (CLAUSILIIDAE)

Crevice-dwelling land snails emerge only infrequently to theexposed surface, and very little is known about their naturalhistory. Here we report on the biology, life cycle, populationdynamics and longevity of one such species, Cristataria genezarethana,which we studied over a period of three years. C. genezarethana spends 95–98% of its lifetime withinrock crevices. In winter the crevice serves as an egg layingsite, and as a retreat during periods of inactivity. Throughoutsummer it serves for aestivation adults aestivate near CTeviceopenings, young apparently deeper inside. The surface of the rock serves mainly as a lichen-feeding andcopulating site, to which the snails emerge during brief periodsof activity. Both for the onset and for the continuation ofits activity season, C. genezarethana is absolutely dependentupon rain. However, activity ends before the end of the rainyseason, suggesting that aestivation is not merely a direct responseto dry climate. Though the population as a whole was active on each rainy day,no more than 15%–20% of the population were active simultaneously.An individual snail was active, on average, for only 6–12days per year. Population size of the study-rock reached 2000–2900individuals, and mean density was 150–200 snails m². Thissnail carrying capacity of the rock is broadly similar to thatof densely populated bushy habitats (when snail weight is considered).In these dense populations, low mating frequencies and growthinhibition may regulate population size. In all three seasons, the population consisted of two main large,well defined age groups: adults and young. As compared to theadults, the young were active on different parts of the rockand at different times. Although a third, intermediate groupof sub adults was found, it was always very small. A fourthgroup, of juveniles, appeared during winter; later, most ofthem disappeared. We did not observe any shift from the young to the adult sizegroup. This suggests a broadly stable population, with virtuallyno recruitment, in which final growth to adulthood is inhibitedby the adults. Growth was very slow, suggesting that maturityin nature is reached in about 11 years, and that individualslive sixteen years at least. Mortality occurred in all age groups,and about 5% of the population died each year. There was noevidence for heavy predation. Crevices might be a suitable habitat for land snails in whichthe hatching period, and period of juvenile growth, are verylong. (Received 1 February 1993; accepted 27 March 1993)     

Emergence of a superradiation: pselaphine rove beetles in mid‐Cretaceous amber from Myanmar and their evolutionary implications

Pselaphinae is an exceptionally species‐rich, globally distributed subfamily of minute rove beetles (Staphylinidae), many of which are inquilines of social insects. Deducing the factors that drove pselaphine diversification and their evolutionary predisposition to inquilinism requires a reliable timescale of pselaphine cladogenesis. Pselaphinae is split into a small and highly plesiomorphic supertribe, Faronitae, and its sister group, the ‘higher Pselaphinae’ – a vast multi‐tribe clade with a more derived morphological ground plan, and which includes all known instances of inquilinism. The higher Pselaphinae is dominated by tribes with a Gondwanan taxonomic bias. However, a minority of tribes are limited to the Nearctic and Palearctic ecozones, implying a potentially older, Pangaean origin of the higher Pselaphinae as a whole. Here, I describe fossils from mid‐Cretaceous (～99 million years old) Burmese amber that confirm the existence of crown‐group higher pselaphines on the Eurasian supercontinent prior to contact with Gondwanan landmasses. Protrichonyx rafifrons gen. et sp.n. is placed incertae sedis within the higher Pselaphinae. Boreotethys gen.n. , erected for B. grimaldii sp.n . and B. arctopteryx sp.n. , represents an extinct sister taxon and putative stem group of Bythinini, a Recent tribe with a primarily Holarctic distribution. The Laurasian palaeolocality of the newly described taxa implies that higher pselaphines are indeed probably of Jurassic, Pangaean extraction and that the Laurasian‐Gondwanan tribal dichotomy of this clade may have developed vicariantly following Pangaean rifting. Higher pselaphines probably predate the earliest ants. Their physically protective morphological ground plan may have been a preadaptation for myrmecophily when ants became diverse and ecologically ubiquitous, much later in the Cenozoic. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:36E3FE2A-B947-422D-89CA-0EF43B99C382 .     

Population Structure of Tundra Swans Wintering in Eastern North America

ABSTRACT Our objective was to determine whether there were subpopulations within the eastern population of tundra swans (Cygnus columbianus columbianus) wintering along the mid-Atlantic coast. Movement rates between regions were substantial enough to result in continual mixing of wintering birds. Thus, we were unable to identify distinct subpopulations based on exclusive use of specific wintering areas. These birds should therefore be monitored, and their harvest managed, as if they were one population.     

Phylogeny and classification of Cucujoidea and the recognition of a new superfamily Coccinelloidea (Coleoptera: Cucujiformia)

A large‐scale phylogenetic study is presented for Cucujoidea (Coleoptera), a diverse superfamily of beetles that historically has been taxonomically difficult. This study is the most comprehensive analysis of cucujoid taxa to date, with DNA sequence data sampled from eight genes (four nuclear, four mitochondrial) for 384 coleopteran taxa, including exemplars of 35 (of 37) families and 289 genera of Cucujoidea. Maximum‐likelihood analyses of these data present many significant relationships, some proposed previously and some novel. Tenebrionoidea and Lymexyloidea are recovered together and Cleroidea forms the sister group to this clade. Chrysomeloidea and Curculionoidea are recovered as sister taxa and this clade (Phytophaga) forms the sister group to the core Cucujoidea (Cucujoidea s.n .). The nitidulid series is recovered as the earliest‐diverging core cucujoid lineage, although the earliest divergences among core Cucujoidea are only weakly supported. The cerylonid series (CS) is recovered as monophyletic and is supported as a major Cucujiform clade, sister group to the remaining superfamilies of Cucujiformia. Currently recognized taxa that were not recovered as monophyletic include Cucujoidea, Endomychidae, Cerylonidae and Bothrideridae. Biphyllidae and Byturidae were recovered in Cleroidea. The remaining Cucujoidea were recovered in two disparate major clades: one comprising the nitidulid series + erotylid series + Boganiidae and Hobartiidae + cucujid series, and the other comprising the cerylonid series. Propalticidae are recovered within Laemophloeidae. The cerylonid series includes two major clades, the bothriderid group and the coccinellid group. Akalyptoischiidae are recovered as a separate clade from Latridiidae. Eupsilobiinae are recovered as the sister taxon to Coccinellidae. In light of these findings, many formal changes to cucujiform beetle classification are proposed. Biphyllidae and Byturidae are transferred to Cleroidea. The cerylonid series is formally recognized as a new superfamily, Coccinelloidea stat.n. Current subfamilies elevated (or re‐elevated) to family status include: Murmidiidae stat.n. , Teredidae stat.n. , Euxestidae stat.n. , Anamorphidae stat.rev. , Eupsilobiidae stat.n. , and Mycetaeidae stat.n. The following taxa are redefined and characterized: Cleroidea s.n. , Cucujoidea s.n. , Cerylonidae s.n. , Bothrideridae s.n. , Endomychidae s.n. A new subfamily, Cyclotominae stat.n. , is described. Stenotarsinae syn.n. is formally subsumed within a new concept of Endomychinae s.n.     

Water balance in the sugarbeet root maggot Tetanops myopaeformis,during long‐term low‐temperature storage and after freezing

The sugarbeet root maggot Tetanops myopaeformis Röder (Diptera: Ulidiidae) can be stored in moist sand at 4–6 °C for up to 5 years and is freeze‐tolerant. The majority of stored larvae survive in a state of post‐diapause quiescence and the remainder are in a multi‐year diapause. The present study aims to determine larval water content and water loss rates in diapausing and low‐temperature stored larvae. Body water content ranges from 57% to 70.1%. Two distinct groupings of larvae are revealed based on dry weights. The first group consists of the diapausing larvae and larvae stored for 1 year. This group has significantly higher dry weights than the second grouping, which consists of the larvae stored for 2 and 3 years. There are no significant differences within each group. Larval water losses follow a first‐order kinetic relationship with time. Larvae stored for 2 years lose water at a significantly higher rate than diapausing larvae. Larvae exhibit no active water uptake at storage temperatures. A freezing event does not induce a significant decrease in wet weights, nor does it increase larval water loss rates. These results indicate that metabolic water and the microclimate during storage are key factors enabling the long‐term survival of T. myopaeformis larvae during low‐temperature storage, and may provide insights for maintaining other insect species under similar conditions.     

Separation of Epstein-Barr Virus DNA from Large Chromosomal DNA in Non-virus-producing Cells

AT least four established human lymphocyte cell lines, one that originates from a Burkitt's lymphoma and the others from normal persons, contain Epstein-Barr virus (EBV) genome¹. These cells show no viral antigens by immunofluorescence tests nor do they produce virus particles. We are examining one of the four cell lines, Raji (cells from a Burkitt's lymphoma), in more detail. The DNA isolated from purified Raji chromosomes contains as much virus genome as the DNA extracted from whole cells (65 genome equivalents per cell)¹. The viral DNA therefore seems to be in the chromosomes. This result, however, does not necessarily indicate that the viral DNA is physically integrated into chromosomal DNA. The following experiments suggest that the EBV DNA in Raji cells is not covalently linked to the large chromosomal DNA, although the number of viral genomes per cell remains constant during passage. The results do not, however, exclude the possibility that small fragments of cell DNA are bonded to the viral DNA. The data also indicate that EBV DNA in Raji cells exists in strands of complete or nearly complete size.