Oogamy: inventing the sexes

The male-female dichotomy has evolved independently in nearly all lineages of multicellular organisms. Why this should be the case is still uncertain, but recent studies of mating-type genes in green algae open a promising new way to explore molecular-genetic aspects of the evolution of dichotomous sexes.     

Sexual conflict: the battle of the sexes reversed

In most species one sex is more reluctant to mate than the other. Standard explanations invoking potential reproductive rates have shortcomings that are illustrated by a new study of eager female and reluctant male antelopes.     

A uniquely conserved regulatory signal is found around the translation initiation site in three different collagen genes

We have determined the nucleotide sequence of the 5' untranslated region and the sequence encoding the signal peptide for mRNAs of the chick alpha 1 type I and alpha 1 type III collagen. These sequences were obtained by synthesizing the corresponding cDNAs using as primers either a synthetic oligonucleotide to prime alpha 1 type I cDNA or a DNA fragment isolated from a genomic clone coding for alpha 1 type III collagen to prime the cognate cDNA. Both primers were selected so that the resulting cDNAs would be short and would contain sequence information for the 5' untranslated region and the signal peptide of the proteins. The nucleotide sequences of these cDNAs were compared with the corresponding sequence of alpha 2 type I collagen. In each mRNA the 5' untranslated segment is approximately 130 nucleotides and contains two or more AUG triplets preceding the AUG which serves as a translation initiation codon. A sequence of about 50 nucleotides surrounding the translation initiation codon is remarkably conserved in all three mRNAs, whereas the sequences preceding and following this segment diverge markedly. This homologous sequence contains an almost identical inverted repeat sequence which could form a stable stem-loop structure. The initiation codon and the AUG which precedes it are found at the same place within this symmetrical sequence and the distance between them is invariant. The rest of the conserved sequence shows a less perfect symmetry. This conserved sequence has not been found in other genes. Our data suggest that these three and perhaps other collagen genes contain an identical regulatory signal that may play a role in determining the level of expression of these genes by modulating translational efficiency.     

Evolutionary novelty in communication between the sexes

The diversity of signalling traits within and across taxa is vast and striking, prompting us to consider how novelty evolves in the context of animal communication. Sexual selection contributes to diversification, and here we endeavour to understand the initial conditions that facilitate the maintenance or elimination of new sexual signals and receiver features. New sender and receiver variants can occur through mutation, plasticity, hybridization and cultural innovation, and the initial conditions of the sender, the receiver and the environment then dictate whether a novel cue becomes a signal. New features may arise in the sender, the receiver or both simultaneously. We contend that it may be easier than assumed to evolve new sexual signals because sexual signals may be arbitrary, sexual conflict is common and receivers are capable of perceiving much more of the world than just existing sexual signals. Additionally, changes in the signalling environment can approximate both signal and receiver changes through a change in transmission characteristics of a given environment or the use of new environments. The Anthropocene has led to wide-scale disruption of the environment and may thus generate opportunity to directly observe the evolution of new signals to address questions that are beyond the reach of phylogenetic approaches.     

Spatial working memory in rats: no differences between the sexes

In a number of mammalian species, males appear to have superior spatial abilities to females. The favoured explanations for this cognitive difference are hormonal, with higher testosterone levels in males than females leading to better spatial performance, and evolutionary, where sexual selection has favoured males with increased spatial abilities for either better navigational skills in hunting or to enable an increased territory size. However, an alternative explanation for this sex difference focuses on the role of varying levels of oestrogen in females in spatial cognition (the 'fertility and parental care' hypothesis). One possibility is that varying oestrogen levels result in variation in spatial learning and memory so that, when tested across the oestrous cycle, females perform as well as males on days of low oestrogen but more poorly on days of high oestrogen. If day in the oestrous cycle is not taken into account then, across an experiment, any sex differences found would always produce male superiority. We used a spatial working memory task in a Morris water maze to test the spatial learning and memory abilities of male and female rats. The rats were tested across a number of consecutive days during which the females went through four oestrous cycles. We found no overall sex differences in latencies to reach a submerged platform in a Morris water maze but, on the day of oestrus (low oestrogen), females took an extra swim to learn the platform's location (a 100% increase over the other days in the cycle). Female swim speed also varied across the oestrous cycle but females were no less active on the day of oestrus. These results oppose the predictions of the fertility and parental care hypothesis.     

Genital Evolution: blurring the battle lines between the sexes

The rapid, divergent evolution of genitalia is a general trend in animals and likely influenced by sexual selection. Contrary to previous ideas, an intriguing new study suggests that sexual selection by sexual conflict can promote the evolution of both male and female genitalia.     

Battle of the sexes over paternity

Reproductive behaviors have evolved through severe inter-sexual competition. We have recently described a behavior in post-mated female Drosophila melanogaster that controls ejaculate retention and sperm storage, and is a possible mechanism by which females who have mated with several partners can choose which sperm that is stored and used for fertilization. This behavior can also regulate exposure of the female to harmful effects of male SFP that are present in the ejaculate. Our study identified the neural pathway functioning in the female brain that regulates this behavior. [BMB Reports 2015; 48(5): 241-242]     

An evolutionary 'intermediate state' of mitochondrial translation systems found in Trichinella species of parasitic nematodes: co-evolution of tRNA and EF-Tu

EF-Tu delivers aminoacyl-tRNAs to ribosomes in the translation system. However, unusual truncations found in some animal mitochondrial tRNAs seem to prevent recognition by a canonical EF-Tu. We showed previously that the chromadorean nematode has two distinct EF-Tus, one of which (EF-Tu1) binds only to T-armless aminoacyl-tRNAs and the other (EF-Tu2) binds to D-armless Ser-tRNAs. Neither of the EF-Tus can bind to canonical cloverleaf tRNAs. In this study, by analyzing the translation system of enoplean nematode Trichinella species, we address how EF-Tus and tRNAs have evolved from the canonical structures toward those of the chromadorean translation system. Trichinella mitochondria possess three types of tRNAs: cloverleaf tRNAs, which do not exist in chromadorean nematode mitochondria; T-armless tRNAs; and D-armless tRNAs. We found two mitochondrial EF-Tu species, EF-Tu1 and EF-Tu2, in Trichinella britovi. T.britovi EF-Tu2 could bind to only D-armless Ser-tRNA, as Caenorhabditis elegans EF-Tu2 does. In contrast to the case of C.elegans EF-Tu1, however, T.britovi EF-Tu1 bound to all three types of tRNA present in Trichinella mitochondria. These results suggest that Trichinella mitochondrial translation system, and particularly the tRNA-binding specificity of EF-Tu1, could be an intermediate state between the canonical system and the chromadorean nematode mitochondrial system.     

Differential host relations of the sexes in parasitic Hymenoptera

The divergent ontogeny of the male, a unique phenomenon characterizing certain genera of the Aphelinidae, has its physiological bases in the environmental control of sex permitted by the haploid origin of the male and the diploid origin of the female and in the efficiency of the chalcidoid type of spermatheca which, during the process of oviposition, brings the environmentally activated sperm into contact with the egg. This divergence is correlated with the sexual dimorphism and the sexual ditrophism of the early developmental stages. It is psychologically manifested in a number of species by a marked difference in the host relations of the aphelinid female before and after mating. The climax of differential host relations within a species is the production of the female in a coccid host and the production of the male in a lepidopterous host. The aberrant development of the male tends to increase the capacity of the species to survive at low host densities.

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Zusammenfassung Nachdem 1935 die obligatorisch wirtsverschiedene Geschlechterentwicklung bei den parasitischen Hymenopteren entdeckt wurde, ist dieses Phänomen bei ca 80% der bekannten Apheliniden, die in Schildläusen und Mottenschildläusen schmarotzen, gefunden worden. Die Kenntnis dieses Phänomens ermöglichte die Züchtung und Ansiedlung von 2 Arten solcher Parasiten in Californien. Die wirtsverschiedene Geschlechterentwicklung besteht in der aberranten Entwicklungsgeschichte des Männchens sowie der geschlechtsgebundenen Ditrophie mit Dimorphismus der Larvenstadien. Bei einigen Arten ist sie gekoppelt mit psychologischen Unterschieden zwischen begatteten und unbegatteten Weibchen, die dann verschiedene Wirtspräferenzen zeigen. Diese bemerkenswerte Spaltung der Wirtspräferenzen steht wohl teilweise in Zusammenhang mit der Funktion der Spermatheca des Chalcidoiden-Typs, die äußerst empfindlich auf wirtseigene Stimuli anzusprechen pflegt. Es handelt sich um ein Wirts-Beziehungs-Phänomen, welches die Wirtsfindungsrate der Art zu erhöhen pflegt. Die ontogenetischen Abweichungen in der Entwicklung der Männchen dürften zur Phylogenie der Apheliniden in keiner Beziehung stehen.

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Paper No. 1117, University of California Citrus Experiment Station, Riverside, California.     

Congruence between the sexes in preexisting receiver responses

Preexisting receiver biases have been shown to affect how femalesdetect and respond to new conspecific traits in a mate choicecontext. Although preexisting biases have often been discussedin the context of female mate choice, these biases need notbe sex limited. In the genus Xiphophorus, swordtail males possessa sexually selected trait, the sword. Here I consider evidencethat the state of a bias favoring sworded conspecifics maybe generally shared by the sexes in taxa in which the sword has not arisen. In three unsworded species of poeciliid fishes,both males and females prefer members of the other sex withswords. In a fourth species, males and females share the absenceof a response to a sword. This congruity between the sexessuggests that response biases may not be sex limited and thatthe sexes could historically share common mechanisms producingshared mating responses. Alternatively, selection may tendto result in parallel changes in biases in the sexes. Thiswork expands our understanding of receiver biases by usinga phylogenetic approach to examine whether biases are historicallyshared by the sexes and suggests that there can be general congruence between the sexes in such biases.     

Symptomatic differences between the sexes in rural Mexico

This paper addresses the problem of the differential presentation of illness by women and men in two Spiritualist temples and a physician's office situated in rural Mexico. Women's morbidity raises the broader anthropological questions of the interplay between symptomatic expression and women's unequal status in the social structure, their cognitive evaluation of specific life experiences, cultural etiological explanations and Western models of dysphoria. Symptoms presented by patients in different health care delivery sites are compared and case vignettes of patients' illnesses and attributions are presented to demonstrate the ways in which culturally constructed illness attributions and illness expressions comprise a somatic grammar for the articulation of experiential distress. The sick population is compared with a control group of healthy women to highlight the socio-cultural and psychosocial variables that promote illness in women from the same sociocultural strata of rural Mexico. Collective understandings of the role of life events and emotional expression in illness attributions legitimize somatization as a coping style under adverse existential conditions.