THE EVOLUTION OF PHENOTYPIC CORRELATIONS AND “DEVELOPMENTAL MEMORY”

Development introduces structured correlations among traits that may constrain or bias the distribution of phenotypes produced. Moreover, when suitable heritable variation exists, natural selection may alter such constraints and correlations, affecting the phenotypic variation available to subsequent selection. However, exactly how the distribution of phenotypes produced by complex developmental systems can be shaped by past selective environments is poorly understood. Here we investigate the evolution of a network of recurrent nonlinear ontogenetic interactions, such as a gene regulation network, in various selective scenarios. We find that evolved networks of this type can exhibit several phenomena that are familiar in cognitive learning systems. These include formation of a distributed associative memory that can “store” and “recall” multiple phenotypes that have been selected in the past, recreate complete adult phenotypic patterns accurately from partial or corrupted embryonic phenotypes, and “generalize” (by exploiting evolved developmental modules) to produce new combinations of phenotypic features. We show that these surprising behaviors follow from an equivalence between the action of natural selection on phenotypic correlations and associative learning, well‐understood in the context of neural networks. This helps to explain how development facilitates the evolution of high‐fitness phenotypes and how this ability changes over evolutionary time.     

COMPETITION BETWEEN SEGREGATION DISTORTERS: COEXISTENCE OF “SUPERIOR” AND “INFERIOR” HAPLOTYPES AT THE t COMPLEX

By means of population genetical models, we investigate the competition between sex-specific segregation distorters. Although the models are quite general, they are motivated by a specific example, the t complex of the house mouse. Some variants at this gene complex, the t haplotypes, distort Mendelian segregation in heterozygous males in their favor. The selective advantage at the gamete level is counterbalanced by strong negative fitness effects at the individual level (male sterility or even lethality in both sexes). A plethora of different t haplotypes has been found, both in the field and in the lab. Up to now, however, models have focused on the equilibrium frequency of a single t haplotype. In contrast, we explicitly model the competition between several t haplotypes. A deterministic model for a large, well-mixed population predicts a surprisingly high degree of polymorphism. Haplotypes with seemingly inferior fitness characteristics may easily coexist with “superior” haplotypes. For instance, a lethal haplotype with a low segregation ratio may stably coexist with a sterile haplotype with a high segregation ratio. Stable coexistence is even possible for haplotypes with a segregation disadvantage. A simple stochastic model shows that the same principles apply in the context of a structured metapopulation. Although counterintuitive at first sight, all our results can be explained by the fact that segregation distorters have an inherent advantage when they are rare. We conclude that fitness comparisons are not sufficient to predict the outcome of competition when selective forces are acting at different levels.     

HOST POPULATION STRUCTURE AND THE EVOLUTION OF VIRULENCE: A “LAW OF DIMINISHING RETURNS”

Structure in a population of host individuals, whether spatial or temporal, can have important effects on the transmission and evolutionary dynamics of its pathogens. One of these is to limit dispersal of pathogens and thus increase the amount of contact between a given pair or within a small group of host individuals. We introduce a “law of diminishing returns” that predicts an evolutionary decline of pathogen virulence whenever there are on average more possibilities of pathogen transmission between the same pair of hosts. Thus, the effect of repeated contact between hosts will be to shift the balance of any trade-off between virulence and transmissibility toward lower virulence.     

SELECTION AND THE “SEX-RATIO” POLYMORPHISM IN NATURAL POPULATIONS OF DROSOPHILA PSEUDOOBSCURA

“Sex-ratio” (SR) is a naturally occurring X-linked meiotic drive system, where the SR-X chromosome is transmitted to nearly all progeny of SR males. It occurs at frequencies of up to 25% in some populations of Drosophila pseudoobscura. Because of the twofold drive advantage, SR should rapidly fix in populations, causing the extinction of the species, unless opposed by strong selection. I examine several of the adult components of fitness, including the frequencies of all genotypic mating combinations, fertilities, and fecundities of flies from two populations in southeastern Arizona. Significant reduction of fecundity of SR/SR females was observed in the Tucson population. No evidence was found for either lower fertility or reduced mating success of SR males, relative to standard males. Most selection opposing SR appears to be operating at the larval stages in nature.     

PHYLOGENETIC AFFINITIES OF “CHANTRANSIA” STAGES IN MEMBERS OF THE BATRACHOSPERMALES AND THOREALES (RHODOPHYTA)1

This study evaluated the phylogenetic relationship among samples of “Chantransia” stage of the Batrachospermales and Thoreales from several regions of the world based on sequences of two genes—the plastid‐encoded RUBISCO LSU gene (rbcL) and the nuclear SSU ribosomal DNA gene (SSU rDNA). All sequences of “Chantransia macrospora” were shown to belong to Batrachospermum macrosporum based on both molecular markers, confirming evidence from previous studies. In contrast, nine species are now associated with “Chantransia pygmaea,” including seven species of the Batrachospermales and two of the Thoreales. Therefore, the presence of “C. macrospora” in a stream can be considered reliable evidence that it belongs to B. macrosporum, whereas the occurrence of “C. pygmaea” does not allow the recognition of any particular species, since it is associated with at least nine species. Affinities of “Chantransia” stages to particular taxa were congruent for 70.5% of the samples comparing the rbcL and SSU analyses, which were associated with the same or closely related species for both markers. Sequence divergences have been reported in the “Chantransia” stage in comparison to the respective gametophyte, and this matter deserves further attention.     

GAMETOGENESIS AND GAMETE RELEASE OF ULVA MUTABILIS AND ULVA LACTUCA (CHLOROPHYTA): REGULATORY EFFECTS AND CHEMICAL CHARACTERIZATION OF THE “SWARMING INHIBITOR”1

Gametophytes of Ulva mutabilis Føyn and Ulva lactuca L. were artificially induced to form gametangia by removal of sporulation inhibitors. After this treatment, U. mutabilis gametes were ready for swarming on the third morning after induction, while U. lactuca gametangia needed 1–2 d longer for maturation. Release of gametes of U. lactuca was dependent solely upon exposure to the first light in the morning. Gametangia of U. mutabilis, however, also required sufficient dilution of the swarming inhibitor (SWI). SWI was excreted transiently by both Ulva species early during gametogenesis. While the SWI concentration in U. mutabilis medium remained above the inhibitory concentration until the gametangia were mature, the concentration of U. lactuca‐SWI dropped rapidly below this level. In the presence of sufficient SWI, mature gametes of U. mutabilis remained motionless within the gametangia despite light and open exit pores. However, using SEM, an additional seal was detected within these pores, which probably prevented premature swarming until dilution of SWI and exposure to light. Observations by time lapse microscopy and experiments with the myosin kinase inhibitor BDM suggest that the gametes may be either extruded by the gametangium or leave the exit pore by active gliding motion, driven by a myosin‐like motor protein. The SWIs were purified from both Ulva species, and mass spectral analysis showed their molecular masses (292 Da) were identical.     

THE EFFECT OF CORPORA ALLATA ON SEXUAL BEHAVIOUR AND “ADULT DIAPAUSE” IN MALES OF THE RED LOCUST

Males of the red locust, Nomadacris septemfasciata, allatectomized 3–11 days after the moult to the adult stage did not exhibit any sexual behaviour and remained in a state comparable to adult diapause, while all the sham-allatectomized controls exhibited distinct sexual behaviour. Implantations of four pairs of active corpora allata (originating from sexually mature males of Locusta migratoria migratorioides) into the allatectomized males of the red locust led to sexual behaviour; in contrast, all those allatectomized males in which shamimplantations (appropriate surgical treatment without actual implantation of corpora allata) were performed remained in adult diapause showing no sexual behaviour.Comparison of the results with other data revealed that in some species of Acridids the corpora allata completely control (in a direct or indirect manner) male sexual behaviour, while in other species of the same family this control is either incomplete or perhaps does not exist at all. The presence or absence of a complete endocrine control of male sexual behaviour may perhaps be correlated with the fact that the species involved has or has not the ability to undergo a state of adult diapause.

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Zusammenfassung Männchen der Roten Heuschrecke, Nomadacris septemfasciata, die 3–11 Tage nach der Häutung zur Imago allatektomiert worden waren, zeigten keinerlei sexuelle Aktivität und verharrten in einem der Adult-Diapause vergleichbaren Zustand, während alle scheinallatektomierten Kontrolltiere ausgeprägtes Sexualverhalten aufwiesen. Implantationen von 4 Paar Corpora allata (aus geschlechtsreifen Männchen von Locusta migratoria migratorioides stammend) in allatektomierte Männchen der Roten Heuschrecke führten zu Sexualverhalten; im Gegensatz dazu verharrten alle diejenigen allatektomierten Männchen, bei welchen Schein-Implantationen durchgeführt wurden (entsprechende operative Behandlung ohne Implantation von Corpora allata) in Adult-Diapause und zeigten keine sexuelle Aktivität.Vergleich der Ergebnisse mit anderen Daten lassen erkennen, daß bei einigen Acridier-Arten die Corpora allata das männliche Sexualverhalten (auf direkte oder indirekte Weise) beeinflussen, während dieser Einfluß bei anderen Arten der gleichen Familie entweder unvollständig ist oder überhaupt nicht auftritt. Vorkommen oder Fehlen einer vollständigen endokrinen Kontrolle des männlichen Sexualverhaltens mag vielleicht von dem Umstand abhängen, ob die betreffende Art die Fähigkeit hat, ein Stadium adulter Diapause zu durchlaufen oder nicht.

     

RESPONSES BY FEMALE DACINAE TO “MALE” LURES AND THEIR RELATIONSHIP TO PATTERNS OF MATING BEHAVIOUR AND PHEROMONE RESPONSE

In laboratory experiments virgin female Dacus sp. A D. aquilonis and D. tenuifascia exhibited significant responses to the chemical lures normally attractive to males of these species (methyl eugenol and cue lure). Development of the female response was correlated with the time course of ovarian maturation. Females did not respond after having mated. Temporal aspects of the female response were analogous to the pheromone responses normally displayed by virgins in the laboratory. It is suggested that the chemicals used as male lures or others related to them are involved in the pheromone communication system of these species although the nature of this involvement is not clear.

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Zusammenfassung In Laboratoriumsversuchen zeigten unbegattete Weibchen von Dacus sp. A, D. aquilionis und D. tenuifascia gesicherte Reaktionen auf chemische Köder, welche normalerweise auf Männchen wirken (Methyleugenol und Cue Lure). Die Entwicklung der Reaktion der Weibchen war korreliert mit dem zeitlichen Verlauf der Eireifung. Die Weibchen reagierten nach der Begattung nicht mehr. Der zeitliche Verlauf der Reaktion der Weibchen war analog der Reaktion unbegatteter Weibchen auf Pheromon im Laboratorium. Es wird angenommen, dass chemische Substanzen, welche als Männchenköder verwendet werden oder diesen ähnlich sind, im Pheromonübermittlungssystem der Art beteiligt sind. Allerdings ist die Art dieser Beteiligung unklar.

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THE INTERACTION OF BEHAVIORAL AND MORPHOLOGICAL CHANGE IN THE EVOLUTION OF A NOVEL LOCOMOTOR TYPE: “FLYING” FROGS

“Flying” frogs have evolved independently several times among anurans. In all cases flyers are distinguished from their nonflying arboreal relatives by a unique set of morphological features and behavioral postures. Using both live animal field tests and wind tunnel models, this study examines the importance of this characteristic morphology and limb position on five aerial performance variables: horizontal traveling distance, minimum glide speed, maximum time aloft, maneuverability, and stability. Comparison of relative performance between a model frog with a generalized nonflying morphology and limb position and a model frog with flying morphology and limb position reveals that the morphological and positional features associated with “flying” actually decrease horizontal traveling distance but improve maneuverability. This finding suggests that maneuverability rather than horizontal travel may be the key performance parameter in the evolution of “flying” frogs. More generally, this study illustrates that (1) derived morphological and postural features do not necessarily change a suite of performance variables in the same way, and (2) the performance consequences of postural shifts are a function of morphology. These findings indicate that the potential complexity of morphological and behavioral interactions in the evolution of new adaptive types is much greater than previously considered.