Differential Processing of Gaze Cueing from a Congruent and Incongruent Informant

Infants are known to be sensitive to, and be capable of, processing social information from birth. However, less is known about abilities related to actively choosing the information source on which to rely, over passively processing all available information. A recent study showed that 8-month-olds’ gaze following behaviour was influenced by the reliability of the informant (Tummeltshammer et al., 2014), suggesting that infants as young as 8 months of age might recognize whether the person in front of them is trustworthy. To better understand this discriminative ability of infants, the current study utilizes event-related potentials (ERPs), to investigate whether infants’ neural activity indicates the differentiation of a congruent informant (who always gives the correct gaze cue to the object location) from an incongruent informant (who only gives the correct gaze cue on 25% of trials). 9-month-old infants (N = 21) were presented with 32 static images in total which showed two female experimenters (16 images for each), one of whom looked at the object appearing on one of the corners 100% of the time (i.e. congruent informant) and the other only looked at the object 25 % of the time and looked away from the object 75% of the time (i.e. incongruent informant). A paired-sample t-test comparing between the congruent and incongruent informants showed that the amplitude of the negative deflection occurring at approximately 275ms post-stimuli over fronto-central regions was enhanced while infants were processing information given by a congruent informant (M= -15.05[µV], SD= 4.56), compared to when the information was given by an incongruent informant (M= -12.35[µV], SD= 3.79) (t= -2.49, p= .002). Previous studies have shown that a negative amplitude component occurring at around 400ms post-stimuli in 9-month infants (the negative component, or the Nc), has been associated with infants’ attentional allocation (e.g. Striano et al., 2006; Parise et al., 2008). While the negative peak observed in the present study is at an earlier latency than the Nc, this indicates a difference in neural processing of congruent and incongruent informants in 9-month-old infants. Furthermore, an enhanced positive slow wave (PSW) over fronto-temporal regions was observed for an incongruent informant (M= 9.27[µV], SD= 5.32) compared to a congruent informant (M= 6.12[µV], SD= 5.63) (t= -2.309, p=.003). As the PSW has been thought to reflect memory updating (Snyder, Webb & Nelson, 2002; Reid et al. 2004), this might reflect how infants alter their perception about the congruency of gaze cues during the short exposure to the information (16 per condition). In sum, the result demonstrates how quickly young infants can recognize the congruency of other people’s gaze cues. This study extends our understanding forward on how infants collect and process social information, as the current study offers evidence that infants as young as 9 months of age selectively process sources of information differentially in the social domain, which might enable them to learn efficiently at a social situation despite ample and complex information present

Coexistence of diploid and triploid hybrid water frogs: population differences persist in the apparent absence of differential survival

Background: The role of differential selection in determining the geographic distribution of genotypes in hybrid systems has long been discussed, but not settled. The present study aims to asses the importance of selection in structuring all-hybrid Pelophylax esculentus populations. These populations, in which the parental species (P. lessonae with genotype LL and P. ridibundus with genotype RR) are absent, have pond-specific proportions of diploid (LR) and triploid (LLR and LRR) genotypes. Results: With data from 12 Swedish ponds, we first show that in spite of significant changes in genotype proportions over time, the most extreme ponds retained their differences over a six year study period. The uneven distribution of genotypes among ponds could be a consequence of differential selection varying among ponds (selection hypothesis), or, alternatively, of different gamete production patterns among ponds (gamete pattern hypothesis). The selection hypothesis was tested in adults by a six year mark-recapture study in all 12 ponds. As the relative survival and proportion of LLR, LR and LRR did not correlate within ponds, this study provided no evidence for the selection hypothesis in adults. Then, both hypotheses were tested simultaneously in juvenile stages (eggs, tadpoles, metamorphs and one year old froglets) in three of the ponds. A gradual approach to adult genotype proportions through successive stages would support the selection hypotheses, whereas the presence of adult genotype proportions already at the egg stage would support the gamete pattern hypothesis. The result was a weak preference for the gamete pattern hypothesis. Conclusions: These results thus suggest that selection is of little importance for shaping genotype distributions of all-hybrid populations of P. esculentus, but further studies are needed for confirmation. Moreover, the study provided valuable data on genotype-specific body lengths, adult survival and sex ratios

Can neural activities during the traditional Piagetian AB search task explain infants’ perseverative search error? : Preliminary results

Since the infant perseverative error (AB error) was first reported by Piaget in 1954, these findings have been well replicated. Yet there is no general agreement on why the error occurs and what aspect of infants’ cognition AB error reflects. Since looking and reaching measures have yielded mixed evidence of infant ability, neurological measures indexing online cognitive processes may shed light on the mechanisms underlying the error, clarifying how different experimental manipulations may highlight different aspects of infants’ cognition involved in the error. In this pilot study, we monitored neural activities while infants engaged in the task in a live setting. We tested 50 9-month-old infants and the final sample consisted of the data from 36 infants. EEG data collected during a 5-second delay period between infants’ observing the toy being hidden and their being allowed to search were grouped into 4 conditions according to the phase (A- or B-trial) and their performance (accurate or inaccurate). The result indicated that theta-band oscillatory activities might perhaps predict infants’ search performance. However, due to the small number of data and large individual differences, none of the statistical comparisons found a significant difference across conditions. Nevertheless, a methodological procedure and analysis pipeline for future EEG research using a live AB task has been established. This pilot study has positioned us ready to untangle a complex cognitive process involved in a behavioural task such as this AB search task utilising a neurological measure

Data from: Post-zygotic selection against parental genotypes during larval development maintains all-hybrid populations of the frog Pelophylax esculentus

Background: Hybridization between two species usually leads to inviable or infertile offspring, due to endogenous or exogenous selection pressures. Yet, hybrid taxa are found in several plant and animal genera, and some of these hybrid taxa are ecologically and evolutionarily very successful. One example of such a successful hybrid is the water frog, Pelophylax esculentus which originated from matings between the two species P. ridibundus (genotype RR) and P. lessonae (LL). At the northern border of the distribution all-hybrid populations consisting of diploid (LR) and one or two triploid (LLR, LRR) frog types have been established. Here, the hybrid has achieved reproductive independence from its sexual ancestors and forms a self-sustaining evolutionary unit. Based on the gamete production of these hybrids, certain mating combinations should lead to LL and RR offspring, but these parental forms are absent among the adults. Results: In order to investigate the mechanisms that maintain such an all-hybrid system, we performed a field study and a crossing experiment. In the field we sampled several ponds for water frog larvae at different developmental stages. Genotype compositions were then analysed and life-history differences between the genotypes examined. In the experiment we crossed diploid and triploid males and females from different ponds and determined fertilization success as well as development speed and survival rates of the offspring under high, medium and low food availability. In both parts of the study, we found numerous LL and RR offspring during the egg and early larval stages; but the frequency of these parental genotypes decreased drastically during later stages. In natural ponds almost all of them had disappeared already before metamorphosis; under the more benign experimental conditions the last ones died as juveniles during the following year. Conclusions: From the combined results we conclude that the absence of parental genotypes in all-hybrid populations is due to post-zygotic selection against them, rather than to pre-zygotic mechanisms that might prevent their formation in the first place. For this post-zygotic selection, genetic mechanisms resulting from low genetic diversity and fixation of deleterious mutations seem to be a more likely explanation than ecological factors

Post-zygotic selection against parental genotypes during larval development maintains all-hybrid populations of the frog Pelophylax esculentus

Background: Hybridization between two species usually leads to inviable or infertile offspring, due to endogenous or exogenous selection pressures. Yet, hybrid taxa are found in several plant and animal genera, and some of these hybrid taxa are ecologically and evolutionarily very successful. One example of such a successful hybrid is the water frog, Pelophylax esculentus which originated from matings between the two species P. ridibundus (genotype RR) and P. lessonae (LL). At the northern border of the distribution all-hybrid populations consisting of diploid (LR) and one or two triploid (LLR, LRR) frog types have been established. Here, the hybrid has achieved reproductive independence from its sexual ancestors and forms a self-sustaining evolutionary unit. Based on the gamete production of these hybrids, certain mating combinations should lead to LL and RR offspring, but these parental forms are absent among the adults. Results: In order to investigate the mechanisms that maintain such an all-hybrid system, we performed a field study and a crossing experiment. In the field we sampled several ponds for water frog larvae at different developmental stages. Genotype compositions were then analysed and life-history differences between the genotypes examined. In the experiment we crossed diploid and triploid males and females from different ponds and determined fertilization success as well as development speed and survival rates of the offspring under high, medium and low food availability. In both parts of the study, we found numerous LL and RR offspring during the egg and early larval stages; but the frequency of these parental genotypes decreased drastically during later stages. In natural ponds almost all of them had disappeared already before metamorphosis; under the more benign experimental conditions the last ones died as juveniles during the following year. Conclusions: From the combined results we conclude that the absence of parental genotypes in all-hybrid populations is due to post-zygotic selection against them, rather than to pre-zygotic mechanisms that might prevent their formation in the first place. For this post-zygotic selection, genetic mechanisms resulting from low genetic diversity and fixation of deleterious mutations seem to be a more likely explanation than ecological factors

Reyer_et_al_Fig-6+7a

This file provides the data basis for Table 4a and Figs. 6 and 7a, which analyze and depict tadpole development under different food treatments from the start of the raising Experiment (SURVA0) to shortly before metamorphosis (SURVA10)

Reyer_et_al_Fig-4

This file presents the numbers of gamete types produced by the crossed LR, LLR and LRR males and females. Data base for Table 2 and Fig. 4

Reyer_er_al_Fig-5

Fertilization success and hatching rates of offspring from different crossing types. Data base for Table 3 and Fig. 5

Reyer_et_al_Fig-7b

Number of surviving froglets from shortly after metamorphosis (Aug 04) to the next summer (July 05). The category "Hyb" includes all hybrid types (LR, LLR, LRR) and the category "Par" the two parental species (LL, RR). Data base for Table 4b and Fig. 7b