Speciation through the learning of habitat features.

Learning of environmental features can influence both mating behaviour and the location where young are produced. This may lead to speciation in three steps: (i) colonization of a new habitat, (ii) genetic divergence of the two groups by adaptation to the habitats, and (iii) a decrease of genetic mixing between the lineages (similar to reinforcement). In a previous paper we showed that steps (i) and (ii) occur readily for a wide range of fixed mating and habitat preferences. Here, we study whether this can ultimately lead to speciation through selective changes in these preferences. We show that this indeed occurs, and, furthermore, it is very general: for a large class of models there is selection toward producing young more frequently in the natal habitat. Once habitat preference is strong, there is selection toward stronger assortative mating. Even when steps (i) and (ii) initially fail, genetic divergence may succeed at a later evolutionary stage, after which a decrease of genetic mixing completes speciation. Our results show that speciation by the learning of habitat features is an extremely effective mechanism.

Establishment probability in fluctuating environments: a branching process model.

We study the establishment probability of invaders in stochastically fluctuating environments and the related issue of extinction probability of small populations in such environments, by means of an inhomogeneous branching process model. In the model it is assumed that individuals reproduce asexually during discrete reproduction periods. Within each period, individuals have (independent) Poisson distributed numbers of offspring. The expected numbers of offspring per individual are independently identically distributed over the periods. It is shown that the establishment probability of an invader varies over the reproduction periods according to a stable distribution. We give a method for simulating the establishment probabilities and approximations for the expected establishment probability. Furthermore, we show that, due to the stochasticity of the establishment success over different periods, the expected success of sequential invasions is larger then that of simultaneous invasions and we study the effects of environmental fluctuations on the extinction probability of small populations and metapopulations. The results can easily be generalized to other offspring distributions than the Poisson.

A time-structured analysis of hypothalamically induced increases in self-grooming and activity in the rat.

Stressors and different manipulations of the paraventricular nucleus of the hypothalamus (PVH) increase self-grooming in the rat. To assess the effect of these PVH manipulations on the timing of grooming in relation to other ongoing behavior, the authors describe these behavioral responses by a time-structured model. The authors show the following: (a) Behavior in each treatment group can be described by a semi-Markov model. Effects of treatments can be described as changes in the parameters of this model, which reflect the tendencies to start and stop grooming and other activities. (b) The PVH manipulations increase self-grooming by increasing the tendencies to start grooming or by extending the period during which grooming occurs. (c) Grooming responses are accompanied by an increase in activity. (d) Different PVH manipulations change the temporal structure of behavior differentially, suggesting that distinct mechanisms within the PVH are involved in the precise timing of grooming in relation to other activities.

Time structure of self-grooming in the rat: self-facilitation and effects of hypothalamic stimulation and neuropeptides.

Specific brain manipulations, such as stimulation of the paraventricular nucleus of the hypothalamus (PVH) or injections of neuropeptides, increase self-grooming in the rat. Such manipulations also affect the different movements that constitute grooming. Using models to assess the time structure of these movements, the authors demonstrate that the rules that control the time structure within grooming are different from the ones that control its initiation. This study also showed that grooming is self-facilitating and that different brain manipulations in the same hypothalamic area induce structurally different kinds of grooming. The authors suggest that this part of the hypothalamus is not only involved in setting priorities to grooming, relative to other behaviors, but is also involved in the timing of different grooming components. These findings suggest that different neural mechanisms may be involved in the initiation and internal time structure of grooming.

When did it really start or stop: the impact of censored observations on the analysis of duration.

Behaviour is often described in terms of bout lengths. Because of censoring, some of these bout lengths may only be observed partially. For instance, when observation is finished after a fixed period the end moment of the last bout remains unknown. The only available information on such a bout length is that it exceeds a certain value. This value is the censored observed bout length. Censored data are quite common in ethology, but the problem is often not recognized. Therefore, the well established statistical methods that account for censoring are rarely used in ethology. We report on the consequences of using standard methods instead of methods adjusted to account for censoring. We demonstrate that the usual methods of dealing with censored observations, such as treating them as uncensored observations or omitting them altogether, leads more often to erroneous conclusions. When an unadjusted test is used for testing the equality of two censored samples of bout lengths, the probability of rejecting the null hypothesis when the samples are different is much lower than when an adjusted test is used. Moreover, especially when censoring patterns differ between samples, the probability of wrongly rejecting the null hypothesis may be increased.

Detection of time-inhomogeneity in behavioural processes: tests for multiple abrupt changes in boutlengths.

Behavioural records often contain inhomogeinities. The number of such changes is usually not known beforehand. In this paper a description is given of parametric as well as non-parametric methods to determine the number of abrupt changes in which have been published in several papers in the biological and statistical literature have been gathered and completed here. The use of the test procedures is illustrated by means of examples.

Detection of low dose effects of psychopharmaca: Application of a semi-Marcov model to rhesus monkey behaviour.

Behavioural testing of psycho-active drugs at lower doses is needed for medical applications and for the study of pharmacological brain mechanisms. Sensitive methods to detect effects on the time structure of behaviour are lacking. We propose a procedure based on a description within the framework of continuous time Marcov chain models. This class of models is generalized to account for constraints on the organisation of a motor pattern including the speed at which it is terminated. This leads to semi-Marcov models with transition rates that quickly increase from zero to a constant level. We describe and compare several models. As an application we consider amphetamine effects on infant rhesus monkeys. One of the models is preferred since, besides giving a good fit, it demonstrates consistent amphetamine effects that can be interpreted as short-term effects on motor constraints. Amphitamine also induced more mother-directed behaviour. We give maximum likelihood procedures for behaviour analysis based on the preferred model.