Negative plant-soil feedback in Arabidopsis thaliana: Disentangling the effects of soil chemistry, microbiome, and extracellular self-DNA

Nutrient deficiency, natural enemies and litter autotoxicity have been proposed as possible mechanisms to explain species-specific negative plant-soil feedback (PSF). Another potential contributor to negative PSF is the plant released extracellular self-DNA during litter decay. In this study, we sought to comprehensively investigate these hypotheses by using Arabidopsis thaliana (L.) Heynh as a model plant in a feedback experiment. The experiment comprised a conditioning phase and a response phase in which the conditioned soils underwent four treatments: (i) addition of activated carbon, (ii) washing with tap water, (iii) sterilization by autoclaving, and (iv) control without any treatment. We evaluated soil chemical properties, microbiota by shotgun sequencing and the amount of A. thaliana extracellular DNA in the differently treated soils. Our results showed that washing and sterilization treatments mitigated the negative PSF effect. While shifts in soil chemical properties were not pronounced, significant changes in soil microbiota were observed, especially after sterilization. Notably, plant biomass was inversely associated with the content of plant self-DNA in the soil. Our results suggest that the negative PSF observed in the conditioned soil was associated to increased amounts of soilborne pathogens and plant self-DNA. However, fungal pathogens were not limited to negative conditions, butalso found in soils enhancing A.thaliana growth. In-depth multivariate analysis highlights that the hypothesis of negative PSF driven solely by pathogens lacks consistency. Instead, we propose a multifactorial explanation for the negative PSF buildup, in which the accumulation of self-DNA weakens the plant's root system, making it more susceptible to pathogens.

Memory of social experience affects female fecundity via perception of fly deposits

Background

Animals can exhibit remarkable reproductive plasticity in response  to their social surroundings, with profound fitness consequences. The presence of same-sex conspecifics can signal current or future expected competition for resources or mates. Plastic responses to elevated sexual competition caused by exposure to same-sex individuals have been well-studied in males. However, much less is known about such plastic responses in females, whether this represents sexual or resource competition, or if it leads to changes in investment in mating behaviour and/or reproduction. Here, we used Drosophila melanogaster to measure the impact of experimentally varying female exposure to other females prior to mating on fecundity before and after mating. We then deployed physical and genetic methods to manipulate the perception of different social cues and sensory pathways and reveal the potential mechanisms involved.

Results

The results showed that females maintained in social isolation prior to mating were significantly more likely to retain unfertilised eggs before mating, but to show the opposite and lay significantly more fertilised eggs in the 24h after mating. More than 48h of exposure to other females was necessary for this social memory response to be expressed. Neither olfactory nor visual cues were involved in mediating fecundity plasticity—instead, the relevant cues were perceived through direct contact with the non-egg deposits left behind by other females.

Conclusions

The results demonstrate that females show reproductive plasticity in response to their social surroundings and can carry this memory of their social experience forward through mating. Comparisons of our results with previous work show that the nature of female plastic reproductive responses and the cues they use differ markedly from those of males. The results emphasise the deep divergence in how each sex realises its reproductive success.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01438-5.

Conspecific "gaze following" in bottlenose dolphins

"Gaze following"—when one individual witnesses another shift its orientation, and then re-orients in the same direction—has been observed in a wide range of species. Related work with dolphins has to date focused on human–dolphin interactions. In this conspecific study, we examined a group of dolphins orienting, in passing, to gateways between their pools, as opportunities for witnesses to demonstrate "gaze following". Seven bottlenose dolphins were synchronously videotaped on six underwater cameras, for 21 h over three days, and the recordings analyzed by trained observers. The identities of all animals present, their partner state, and whether and to what degree they had altered their access to the gate (e.g., from Monocular to Binocular, or Binocular to Visio-Echoic) was recorded. Compared to animals that did not witness such a change, witnesses of an increase in access by another dolphin were significantly more likely to also act to increase their own access. We observed 460 such cases of "gaze following" in these animals. Dolphins who were partnered (showed sustained swimming within 1 body length) were significantly more likely, than non-partnered animals, to "gaze follow". Dolphins also showed a significant tendency toward matching the kind of access they observed. No significant difference was found in the presence of animals in the back pools, during changes in orientation that were followed, versus in those that were not. These findings support adding bottlenose dolphins to the growing list of species that display conspecific "gaze following".

Effects of habitat quality on abundance, size and growth of mussel recruits

Recruitment of mussels is a complex process with the successful arrival of individuals hinging on the availability of suitable habitats. We examined the effects of adult mussels as settlement habitat and the degree to which the suitability of habitat they offer is species-specific by comparing the recruitment success of intertidal mussels. We hypothesised that mussel recruitment and early growth are dictated by the quality of habitat offered by conspecifics adults. We used a unique experimental arena on the south coast of South Africa, where Mytilus galloprovincialis and two lineages of Perna perna co-exist. Treatments were based on the translocation of individuals of M. galloprovincialis, western- and eastern lineage of P. perna to a single site, where artificial beds were created and sampled monthly over one year. Recruit's number, their sizes and growth were greater within beds of the western lineage of Perna than eastern lineage or Mytilus beds. The results clearly demonstrate that the quality of settlement habitat offered by adult beds differs among adult lineages/species and affects rates of settlement and the early growth of recruits. This effect extends to the intraspecific level; we found greater differences in density and growth of recruits between lineages of Perna than between either lineage and M. galloprovincialis.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10750-022-04994-7.

Preference for speech in infancy differentially predicts language skills and autism-like behaviors

Early emerging biases for conspecific vocalizations are a hallmark of early development. Typically developing neonates listen to speech more than many other sounds, including non-biological non-speech sounds, but listen equally to speech and monkey calls. By 3 months of age, however, infants prefer speech over both non-biological non-speech sounds and monkey calls. We examined whether different listening preferences continue to develop along different developmental trajectories and whether listening preferences are related to developmental outcomes. Given the static preference for speech over non-biological non-speech sounds and the dynamic preference for speech over monkey calls between birth and 3 months, we examined whether 9-month-olds prefer speech over non-biological non-speech sounds (Experiment 1) and prefer speech over monkey calls (Experiment 2). We compared preferences for sounds in infants at low risk (SIBS-TD) and infants at high risk (SIBS-A) of autism spectrum disorder (ASD), a heterogeneous population who differ from typically developing infants in their preferences for speech, and examined whether listening preferences predict vocabulary and autism-like behaviors at 12 months for both groups. At 9 months, SIBS-TD listened longer to speech than to non-speech sounds and listened longer to monkey calls than to speech, whereas SIBS-A listened longer to speech than to non-speech sounds but listened equally to speech and monkey calls. SIBS-TD's preferences did not predict immediate developmental outcomes. In contrast, SIBS-A who preferred speech over non-speech or monkey calls had larger vocabularies and fewer markers of autism-like behaviors at 12 months, which could have positive developmental implications.

Novel flexibility of social learning in dog puppies

Social learning has a large impact on fitness by reducing the costs and dangers associated with independent learning but little research has been conducted to investigate the ontogeny or individual development of this type of learning. Recent research indicated that puppies demonstrate social learning to both conspecific and human demonstrators, but were also more likely to learn better from an unfamiliar conspecific compared to their mother.

Sniffing out the competition? Juvenile coral reef damselfishes use chemical cues to distinguish the presence of conspecific and heterospecific aggregations

Aquatic animals commonly rely on chemical cues to provide information regarding their surroundings. They can respond either by being attracted to (potential mates, preferred habitats) or avoiding (predators, competitors) the source of the stimuli. Coral reef fishes use chemical cues to detect habitats, avoid predators and recognise conspecifics. However, the extent to which chemical cues are used to detect and respond to potential competitors, has received little attention. Here we test olfactory preferences for conspecifics and heterospecifics in newly settled juvenile coral reef fishes. Juveniles of 4 common coral-associated damselfish species: Dascyllus melanurus, Dascyllus reticulatus, Chrysiptera arnazae and Pomacentrus moluccensis, were subjected to olfactory choice tests. Three of the 4 species (excluding P. moluccensis) demonstrated preferences for waterborne conspecifics odours. All species exhibited an avoidance towards heterospecific odours; this aversion was consistently greatest towards P. moluccensis. A neutral response toward heterospecifics was only evident in two instances (1) between the two congeneric Dascyllus species, with D. melanurus toward D. reticulatus, and (2) with C. arnazae toward D. melanurus. While it is already known that the presence of conspecifics plays a vital role in settlement site selection, we show here that the presence of heterospecifics may also be key in determining the spatial distributions of juveniles across areas of coral reef.

Individuating the neural bases for the recognition of conspecifics with MVPA

Conspecifics are potential mates, and can be the most dangerous threats. With conspecifics we engage in complex social interactions. Therefore, it is important to rapidly detect the presence of conspecifics in a scene. Images of humans attract attention, and do so already in 9-months-old infants, showing that the distinction between conspecifics and other animals emerges early in development. However, despite a wealth of evidence on the behavioral differences between the processing of conspecifics and other animals, the neural mechanisms that underlie the recognition of conspecifics remain unknown. In this experiment, we used recursive feature elimination to individuate brain regions that show selective effects for the faces of conspecifics, individuating reliable conspecific effects in the right ventrolateral prefrontal cortex (vlPFC). Consistent with the importance of conspecifics recognition for reorienting attention and for social cognition, this region shows functional connectivity with the temporo-parietal junction (TPJ), implicated in reorienting attention and in the attribution of mental states to others. Our results suggest that the right vlPFC plays an important role for the recognition of conspecifics and may function as a gateway for the attribution of mental states to an object.