Rolando Rodríguez-Muñoz

Natural and Sexual Selection in a Wild Insect Population

Insects in the Wild Insects are of fundamental importance to terrestrial ecosystems and provide laboratory model systems for the study of physiology and genetics. Studies examining how natural and sexual selection operate to drive evolution in wild populations have often neglected invertebrates, resulting in a chasm between our understandings of how things work in the lab versus the natural environment. Rodríguez-Muñoz et al. (p. 1269; see the Perspective by Zuk) bridge this gap by comprehensively monitoring the life histories, behavior, and reproductive success of an entire population of field crickets. Adding genetic data allowed evaluation of how behavior impacts reproductive success and confirmed that male reproductive success varies more than that of females. Monitoring reproduction in wild crickets confirms that male success varies more than female success. The understanding of natural and sexual selection requires both field and laboratory studies to exploit the advantages and avoid the disadvantages of each approach. However, studies have tended to be polarized among the types of organisms studied, with vertebrates studied in the field and invertebrates in the lab. We used video monitoring combined with DNA profiling of all of the members of a wild population of field crickets across two generations to capture the factors predicting the reproductive success of males and females. The factors that predict a male’s success in gaining mates differ from those that predict how many offspring he has. We confirm the fundamental prediction that males vary more in their reproductive success than females, and we find that females as well as males leave more offspring when they mate with more partners.

Ontogeny of γ‐aminobutyric acid‐immunoreactive neuronal populations in the forebrain and midbrain of the sea lamprey

Although brain organization in lampreys is of great interest for understanding evolution in vertebrates, knowledge of early development is very scarce. Here, the development of the forebrain and midbrain γ‐aminobutyric acid (GABA)‐ergic systems was studied in embryos, prolarvae, and small larvae of the sea lamprey using an anti‐GABA antibody. Ancillary immunochemical markers, such as proliferating cell nuclear antigen (PCNA), calretinin, and serotonin, as well as general staining methods and semithin sections were used to characterize the territories containing GABA‐immunoreactive (GABAir) neurons. Differentiation of GABAir neurons in the diencephalon begins in late embryos, whereas differentiation in the telencephalon and midbrain was delayed to posthatching stages. In lamprey prolarvae, the GABAir populations appear either as compact GABAir cell groups or as neurons interspersed among GABA‐negative cells. In the telencephalon of prolarvae, a band of cerebrospinal fluid‐contacting (CSF‐c) GABAir neurons (septum) was separated from the major GABAir telencephalic band, the striatum (ganglionic eminence) primordium. The striatal primordium appears to give rise to most GABAir neurons observed in the olfactory bulb and striatum of early larval stages. GABAir populations in the dorsal telencephalon appear later, in 15–30‐mm‐long larvae. In the diencephalon, GABAir neurons appear in embryos, and the larval pattern of GABAir populations is recognizable in prolarvae. A small GABAir cluster consisting mainly of CSF‐c neurons was observed in the caudal preoptic area, and a wide band of scattered CSF‐c GABAir neurons extended from the preoptic region to the caudal infundibular recess. A mammillary GABAir population was also distinguished. Two compact GABAir clusters, one consisting of CSF‐c neurons, were observed in the rostral (ventral) thalamus. In the caudal (dorsal) thalamus, a long band extended throughout the ventral tier. The nucleus of the medial longitudinal fascicle contained an early‐appearing GABAir population. The paracommissural pretectum of prolarvae and larvae contained a large group of non‐CSF‐c GABAir neurons, although it was less compact than those of the thalamus, and a further group was found in the dorsal pretectum. In the midbrain of larvae, several groups of GABAir neurons were observed in the dorsal and ventral tegmentum and in the torus semicircularis. The development of GABAergic populations in the lamprey forebrain was similar to that observed in teleosts and in mouse, suggesting that GABA is a very useful marker for understanding evolution of forebrain regions. The possible relation between early GABAergic cell groups and the regions of the prosomeric map of the lamprey forebrain (Pombal and Puelles [ 1999 ] J. Comp. Neurol. 414:391–422) is discussed in view of these results and information obtained with ancillary markers. J. Comp. Neurol. 446:360–376, 2002.

Early development of the retina and pineal complex in the sea lamprey: Comparative immunocytochemical study

Lampreys have a complex life cycle, with largely differentiated larval and adult periods. Despite the considerable interest of lampreys for understanding vertebrate evolution, knowledge of the early development of their eye and pineal complex is very scarce. Here, the early immunocytochemical organization of the pineal complex and retina of the sea lamprey was studied by use of antibodies against proliferating cell nuclear antigen (PCNA), opsin, serotonin, and γ‐aminobutyric acid (GABA). Cell differentiation in the retina, pineal organ, and habenula begins in prolarvae, as shown by the appearance of PCNA‐negative cells, whereas differentiation of the parapineal vesicle was delayed until the larval period. In medium‐sized to large larvae, PCNA‐immunoreactive (‐ir) cells were numerous in regions of the lateral retina near the differentiated part of the larval retina (central retina). A late‐proliferating region was observed in the right habenula. Opsin immunoreactivity appears in the pineal vesicle of early prolarvae and 3 or 4 days later in the retina. In the parapineal organ, opsin immunoreactivity was observed only in large larvae. In the pineal organ, serotonin immunoreactivity was first observed in late prolarvae in photoreceptive (photoneuroendocrine) cells, whereas only a few of these cells appeared in the parapineal organ of large larvae. No serotonin immunoreactivity was observed in the larval retina. GABA immunoreactivity appeared earlier in the retina than in the pineal complex. No GABA‐ir perikaryon was observed in the retina of larval lampreys, although a few GABA‐ir centrifugal fibers innervate the inner retina in late prolarvae. First GABA‐ir ganglion cells occur in the pineal organ of 15–17 mm larvae, and their number increases during the larval period. The only GABA‐ir structures observed in the parapineal ganglion of larvae were afferent fibers, which appeared rather late in development. The time sequence of development in these photoreceptive structures is rather different from that observed in teleosts and other vertebrates. This suggests that the unusual development of the three photoreceptive organs in lampreys reflects specialization for their different functions during the larval and adult periods. J. Comp. Neurol. 442:250–265, 2002.

Ontogeny of γ-aminobutyric acid–immunoreactive neurons in the rhombencephalon and spinal cord of the sea lamprey

The development of neurons expressing γ‐aminobutyric acid (GABA) in the rhombencephalon and spinal cord of the sea lamprey (Petromyzon marinus) was studied for the first time with an anti‐GABA antibody. The earliest GABA‐immunoreactive (GABAir) neurons appear in late embryos in the basal plate of the isthmus, caudal rhombencephalon, and rostral spinal cord. In prolarvae, the GABAir neurons of the rhombencephalon appear to be distributed in spatially restricted cellular domains that, at the end of the prolarval period, form four longitudinal GABAir bands (alar dorsal, alar ventral, dorsal basal, and ventral basal). In the spinal cord, we observed only three GABAir longitudinal bands (dorsal, intermediate, and ventral). The larval pattern of GABAir neuronal populations was established by the 30‐mm stage, and the same populations were observed in premetamorphic and adult lampreys. The ontogeny of GABAergic populations in the lamprey rhombencephalon and spinal cord is, in general, similar to that previously described in mouse and Xenopus. J. Comp. Neurol. 464:17–35, 2003.

Guarding Males Protect Females from Predation in a Wild Insect

Males frequently remain in close proximity to their mate immediately postcopulation. This behavior has generally been interpreted as a guarding tactic designed to reduce the likelihood that a rival male can rapidly displace the ejaculate of the guarding male [1, 2]. Such attempts by males to control their mates represent a potential source of conflict [3-5], but guarding behaviors in species where it is difficult for males to control their mates suggest that conflict is not inevitable [6, 7]. We employed a network of infrared video cameras to study a wild population of individually marked and genotyped field crickets (Gryllus campestris). Lone females or males suffer similar rates of predation, but when a pair is attacked, the male allows the female priority access to their burrow, and in doing so dramatically increases his probability of being killed. In compensation for this increased predation risk, paired males mate more frequently and father more of the females offspring. By staying with a male, females increase the sperm contribution of preferred males as well as reducing their predation risk. In contrast to conclusions based on previous lab studies, our field study suggests that mate guarding can evolve in a context of cooperation rather than conflict between the sexes.

Genetic differentiation of an endangered capercaillie (Tetrao urogallus) population at the Southern edge of the species range

The low-latitude limits of species ranges are thought to be particularly important as long-term stores of genetic diversity and hot spots for speciation. The Iberian Peninsula, one of the main glacial refugia in Europe, houses the southern distribution limits of a number of boreal species. The capercaillie is one such species with a range extending northwards to cover most of Europe from Iberia to Scandinavia and East to Siberia. The Cantabrian Range, in North Spain, constitutes the contemporary south-western distribution limit of the species. In contrast to all other populations, which live in pure or mixed coniferous forests, the Cantabrian population is unique in inhabiting pure deciduous forests. We have assessed the existence of genetic differentiation between this and other European populations using microsatellite and mitochondrial DNA (mtDNA) extracted from capercaillie feathers. Samples were collected between 2001 and 2004 across most of the current distribution of the Cantabrian population. Mitochondrial DNA analysis showed that the Cantabrian birds form a distinct clade with respect to all the other European populations analysed, including the Alps, Black Forest, Scandinavia and Russia, which are all members of a discrete clade. Microsatellite DNA from Cantabrian birds reveals the lowest genetic variation within the species in Europe. The existence of birds from both mtDNA clades in the Pyrenees and evidence from microsatellite frequencies for two different groups, points to the existence of a Pyrenean contact zone between European and Cantabrian type birds. The ecological and genetic differences of the Cantabrian capercaillies qualify them as an Evolutionarily Significant Unit and support the idea of the importance of the rear edge for speciation. Implications for capercaillie taxonomy and conservation are discussed.

GABA immunoreactivity in the olfactory bulbs of the adult sea lamprey Petromyzon marinus L

The distribution of gamma-aminobutyric acid (GABA) immunoreactivity in the olfactory bulbs of the adult sea lamprey was studied using an antibody against this transmitter. Five types of GABA-immunoreactive (GABAir) cells were observed. Medium-sized GABAir cells (periglomerular cells) were located around the olfactory glomeruli and occasionally within them. In the inner cellular layer of the bulbs and around the olfactory ventricles, two types of GABAir perikarya were present: some medium-sized GABAir cells and numerous small GABAir cells (granules). In the walls of the olfactory ventricle, some medium-sized GABAir cells of cerebrospinal fluid-contacting type were observed. At the entrance of the olfactory nerves, medium-sized GABAir bipolar cells were present, mostly located between the olfactory nerve and the glomerular layer or close to the meninges, but some in the intracranial portion of the olfactory nerve. GABAir processes were present in all layers of the olfactory bulb. In addition there were also GABAir cells in the dorsal interbulbar commissure. The distribution of GABA observed in the olfactory system of lampreys indicates that this transmitter plays a major role in the modulation of bulbar circuits. The presence of granular and periglomerular cells in lampreys indicates that these two intrinsic GABAergic neurons of the olfactory bulbs are shared by most vertebrates, although lampreys have additional GABAir cell types.

Male dominance determines female egg laying rate in crickets

A key prediction of theories of differential allocation and sexual conflict is that male phenotype will affect resource allocation by females. Females may adaptively increase investment in offspring when mated to high quality males to enhance the quality of their offspring, or males may vary in their ability to manipulate female investment post-mating. Males are known to be able to influence female reproductive investment, but the male traits underlying this ability have been little studied in taxa other than birds. We investigated the relationship between male dominance and female oviposition rate in two separate experiments using the field cricket, Gryllus bimaculatus. In both experiments, females mated to more dominant (but not larger) males laid more eggs. This reveals that either females allocate more effort to reproduction after mating with a dominant male or that dominance status is associated with male ability to manipulate their mates. This is the first evidence that dominance, rather than male attractiveness, has a post-copulatory effect on reproductive investment by females.

Multiple post‐mating barriers to hybridization in field crickets

Mechanisms that prevent different species from interbreeding are fundamental to the maintenance of biodiversity. Barriers to interspecific matings, such as failure to recognize a potential mate, are often relatively easy to identify. Those occurring after mating, such as differences in the how successful sperm are in competition for fertilisations, are cryptic and have the potential to create selection on females to mate multiply as a defence against maladaptive hybridization. Cryptic advantages to conspecific sperm may be very widespread and have been identified based on the observations of higher paternity of conspecifics in several species. However, a relationship between the fate of sperm from two species within the female and paternity has never been demonstrated. We use competitive microsatellite PCR to show that in two hybridising cricket species, Gryllus bimaculatus and G. campestris, sequential cryptic reproductive barriers are present. In competition with heterospecifics, more sperm from conspecific males is stored by females. Additionally, sperm from conspecific males has a higher fertilisation probability. This reveals that conspecific sperm precedence can occur through processes fundamentally under the control of females, providing avenues for females to evolve multiple mating as a defence against hybridization, with the counterintuitive outcome that promiscuity reinforces isolation and may promote speciation.

Dynamics of among-individual behavioral variation over adult lifespan in a wild insect

Lay Summary Wild crickets show consistent patterns of behavior over their adult lifetimes and as they get older they become increasingly predictable. We tagged crickets and then periodically recaptured them and measured their behavior in the lab. This revealed that rather than variation in how age affects behavior, there were consistent patterns across the whole population. We do not have a situation where some crickets live fast and die young while others take it easy and slow.