Switching Partners Research Articles

A new tool to improve the estimates of interaction rewiring considering the whole community composition

Abstract Understanding temporal dynamics in ecological networks is crucial to predict their capability to cope with global changes. Despite this, proper quantification of network dynamics still remains a challenge. Temporal dynamics are typically studied using data of interaction networks over time, through the evaluation of interaction turnover and its two components: changes related to species turnover (species gains and losses) or rewiring (switching partners among the set of species shared over time). However, with this approach based exclusively on network data, dynamics are computed similarly for species that are truly missing from the community at a given temporal period, and for species occurring in the community but that do not interact with any other. This might lead to an underestimation of the real extent of rewiring, while overestimating the species turnover component of interaction turnover. We used data on 20 plant–pollinator communities to calculate interaction turnover components accounting also for the species that occurred in the communities at different temporal periods but did not appear in some of the temporal interaction networks (non‐interacting species) and then compared these estimates with conventional ones. Besides, we used empirical data and simulations to evaluate the extent to which dynamics estimates were affected by sampling effort when including and excluding non‐interacting species. As expected, disregarding the non‐interacting species that occurred in the communities at different temporal periods led to the underestimation of rewiring and the overestimation of species turnover as components of interaction turnover. Effect size was moderate when independent pollinator data were included, and large when including plants or both trophic levels. Simulations indicated that, in general, considering the non‐interacting species reduced biases at the time of identifying changes due to the different interaction turnover components. Accounting for non‐interacting species was particularly important to reduce bias when sampling effort was low and when dynamics were calculated seasonally. Despite sampling effort effects, phenology was the main determinant of species' rewiring frequencies. Our approach contributes to reducing biases and improving the estimates of interaction flexibility in networks, which are necessary to comprehend the response of communities in the face of global change.

Structural resilience and high interaction dissimilarity of plant-pollinator interaction networks in fire-prone grasslands.

Fire is a frequent disturbance in most grasslands around the world, being key for the structure and dynamics of the biodiversity in such ecosystems. While grassland species may be resilient, little is known on how plant-pollinator networks reassemble after fire. Here, we investigate the structure and dynamics of plant-pollinator networks and the variation in species roles over a 2-year post-fire chronosequence on grassland communities in Southern Brazil. We found that both network specialization and modularity were similar over the chronosequence of time-since-fire, but in freshly burnt areas, there were more species acting as network hubs. Species roles exhibited high variation, with plant and pollinator species shifting roles along the post-disturbance chronosequence. Interaction dissimilarity was remarkably high in networks irrespective of times-since-fire. Interaction dissimilarity was associated more with rewiring than with species turnover, indicating that grassland plant and pollinator species are highly capable of switching partners. Time-since-fire had little influence on network structure but influenced the identity and diversity of pollinators playing key roles in the networks. These findings suggest that pollination networks in naturally fire-prone ecosystems are highly dynamic and resilient to fire with both plants and pollinators being highly capable of adjusting their interactions and network structure after disturbance.

Trust-based partner switching among partitioned regions promotes cooperation in public goods game.

In this paper, the coevolution mechanism of trust-based partner switching among partitioned regions on an adaptive network is studied. We investigate a low-information approach to building trust and cooperation in public goods games. Unlike reputation, trust scores are only given to players by those with whom they have a relationship in the game, depending on the game they play together. A player’s trust score for a certain neighbor is given and known by that player only. Players can adjust their connections to neighbors with low trust scores by switching their partners to other players. When switching partners, players divide other nodes in the network into three regions: immediate neighbors as the known region, indirectly connected second-order neighbors as the intermediate region, and other nodes as the unknown region. Such choices and compartmentalization often occur in global and regional economies. Our results show that preference for switching to partners in the intermediate region is not conducive to spreading cooperation, while random selection has the disadvantage of protecting the cooperator. However, selecting new partners in the remaining two regions based on the average trust score of the known region performs well in both protecting partners and finding potential cooperators. Meanwhile, by analyzing the parameters, we find that the influence of vigilance increasing against unsatisfactory behavior on evolution direction depends on the level of cooperation reward.

Inertia in partnerships: The role of gender

Using a controlled laboratory experiment, we provide rigorous evidence regarding inertia in partnerships. We find people maintain partnerships even when doing so is costly to themselves and brings neither benefits nor costs to their partners. Moreover, we find this effect to be much more pronounced for males than females, suggesting that males incur greater psychological costs of switching partners than do females.

Nest-site fidelity and breeding dispersal by Common Tailorbirds in a tropical forest

BackgroundInformation pertaining to nest-site fidelity and breeding dispersal over successive years can help to better our understanding of how birds respond to nest predation.MethodsBy using mist nets and tracking the color banded individuals, we investigated nest-site fidelity and breeding dispersal by Common Tailorbirds (Orthotomus sutorius) throughout a year and between successive years in 2017–2018.ResultsThe present study showed that Common Tailorbirds could produce up to four clutches per breeding season. When multiple broods were produced within a year, breeding pairs remained together, and the nest rebuilding rate was up to 92.2%, with only four cases (7.8%) in which birds reused their old nests. The dispersal distance between the nests during multiple breeding was found to be 10.0 ± 10.5 m, and nest-site fidelity within the same year was 90.0%. By the second year of breeding, 76.2% of individuals remained in the original breeding pairs, while for those that did switch partners, the females remained in the nest from the previous year and paired with new males. The dispersal distance between years was 26.5 ± 41.9 m, and nest-site fidelity between different years was 80.1%. There was no significant difference between within-year and between-year dispersal distances. Moreover, there was no significant difference in the dispersal distance of rebuilt nests between birds that had experienced nest predation and those that had not.ConclusionsOur findings suggest that Common Tailorbirds maintain a high degree of fidelity to mates and nest-sites, and nest predation had no significant effect on territorial changes or breeding dispersal distance between each breeding attempt.

A PAX5-OCT4-PRDM1 developmental switch specifies human primordial germ cells.

Dysregulation of genetic pathways during human germ cell development leads to infertility. Here, we analyzed bona fide human primordial germ cells (hPGCs) to probe the developmental genetics of human germ cell specification and differentiation. We examined distribution of OCT4 occupancy in hPGCs relative to human embryonic stem cells (hESCs). We demonstrate that development, from pluripotent stem cells to germ cells, is driven by switching partners with OCT4 from SOX2 to PAX5 and PRDM1. Gain- and loss-of-function studies revealed that PAX5 encodes a critical regulator of hPGC development. Moreover, analysis of epistasis indicates that PAX5 acts upstream of OCT4 and PRDM1. The PAX5-OCT4-PRDM1 proteins form a core transcriptional network that activates germline and represses somatic programs during human germ cell differentiation. These findings illustrate the power of combined genome editing, cell differentiation and engraftment for probing human developmental genetics that have historically been difficult to study.

Divorce in the socially monogamous zebra finch: Hormonal mechanisms and reproductive consequences

Up to 80% of all bird species are socially monogamous. Divorce (switching partners) or pair disruption (due to the death of a partner) has been associated with decreased reproductive success, suggesting social monogamy is a strategy that may maximize fitness via coordination between partners. Previous studies have demonstrated the effects of divorce and pair disruption on immediate reproductive success. Here, we used a paired experimental design in the zebra finch (Taeniopygia guttata) to examine the hormonal mechanisms that modulate parental behavior and reproductive success in response to a partnership change (hereafter divorce). Specifically, we examined the effects of divorce on the avian stress hormone corticosterone (CORT) in both parents and nestlings, parental behaviors (incubation and nestling provisioning), prolactin (PRL), and reproductive success. We found that divorce resulted in delayed clutch initiation, reduced clutch mass, and an increase in nestling CORT response to a standardized stressor. These effects on reproductive investment and chick CORT response were not clearly determined by parental endocrine responses. Divorce had no effect on the level of parental CORT. PRL levels were highly correlated within a pair regardless of treatment, were negatively related to the investment that males made in incubation, and increased in experimental males as a result of pair disruption. This study demonstrates the fundamental impact which divorce has not only on reproduction, but also the physiological stress responses of offspring and suggests that in socially monogamous animals the maintenance of a stable partnership over time could be advantageous for long term fitness.

Relational contracts and supplier turnover in the global economy

Headquarters and their specialized component suppliers have a vital interest in establishing long-term collaborations. When formal contracts are not enforceable, such efficiency-enhancing cooperations can be established via informal agreements, but relational contracts have been largely ignored in the literature on the international organization of value chains. In this paper, we develop a dynamic property rights model of global sourcing. A domestic headquarter collaborates with a foreign input supplier and makes two decisions in every period: i) whether to engage in a costly search for a better partner, and ii) whether to make a non-binding offer to overcome hold-up problems. Our key result is that the possibility to switch partners crucially affects the contractual nature of buyer-supplier relationships. In particular, some patient firms do not immediately establish a relational contract, but only when they decide to stop searching and thus launch a long-term collaboration with their supplier. Using firm-product-level data of fresh Chinese exporters to the US, we obtain empirical evidence in line with the predictions of our theory.

'It's Not You, It's Me': Breakups in U.S.-China Trade Relationships

This paper uses confidential U.S. Customs data on U.S. importers and their Chinese exporters toinvestigate the frictions from changing exporting partners. High costs from switching partners can affect the efficiency of buyer-supplier matches by impeding the movement of importers from high to lower cost exporters. I test the significance of this channel using U.S. import data, which identifies firms on both sides (U.S. and foreign) of an international trade relationship, the location of the foreign supplier, and values and quantities for the universe of U.S. import transactions. Using transactions with China from 2003-2008, I find evidence suggesting that barriers to switching exporters are considerable: 45% of arm’s-length importers maintain their partner from one year to the next, and one-third of all switching importers remain in the same city as their original partner. In addition, importers paying the highest prices are the most likely to change their exporting partner. Guided by these empirical regularities, I propose and structurally estimate a dynamic discrete choice model of exporter choice, embedded in a heterogeneous firm model of international trade. In the model, importing firms choose a future partner using information for each choice, but are subject to partner and location-specific costs if they decide to switch their current partner. Structural estimates of switching costs are large, and heterogeneous across industries. For the random sample of 50 industries I use, halving switching costs shrinks the fraction of importers remaining with their partner from 57% to 18%, and this improvement in match efficiency leads to a 12.5% decrease in the U.S.-China Import Price Index.

Concerted hydrogen-bond breaking by quantum tunneling in the water hexamer prism.

The nature of the intermolecular forces between water molecules is the same in small hydrogen-bonded clusters as in the bulk. The rotational spectra of the clusters therefore give insight into the intermolecular forces present in liquid water and ice. The water hexamer is the smallest water cluster to support low-energy structures with branched three-dimensional hydrogen-bond networks, rather than cyclic two-dimensional topologies. Here we report measurements of splitting patterns in rotational transitions of the water hexamer prism, and we used quantum simulations to show that they result from geared and antigeared rotations of a pair of water molecules. Unlike previously reported tunneling motions in water clusters, the geared motion involves the concerted breaking of two hydrogen bonds. Similar types of motion may be feasible in interfacial and confined water.

Gear-like rotation by a wobbly water duo

Hydrogen Bonding The molecules in liquid water move about constantly, but on average they cling to each other through hydrogen bonds, like dancers who keep switching partners. Richardson et al. uncovered a fresh twist in this molecular dance (see the Perspective by Clary). Studying clusters of six

Functional analysis of mutual behavior in laboratory rats (Rattus norvegicus).

Three pairs of rats were trained to synchronize their lever pressing according to a mutual reinforcement contingency, in which alternating lever presses that fell within a 500-ms window were reinforced with food. In Experiment 1, rats worked in adjacent chambers separated by a transparent barrier, and the effects of the mutual reinforcement contingency were compared with those under yoked-control conditions that provided the same rate of food reinforcement but without the temporal coordination response requirement. In Experiment 2, coordinated behavior was compared with and without a barrier, and across different barrier types: transparent, opaque, wire mesh. In Experiment 3, the effects of social familiarity were assessed by switching partners, enabling a comparison of coordinated behavior with familiar and unfamiliar partners. The overall pattern of results shows that the coordinated behavior of 2 rats was (a) maintained by mutual reinforcement contingencies, (b) unrelated to the type or presence of a barrier separating the rats, and (c) sufficiently flexible to adjust to the presence and behavior of an unfamiliar partner. Taken as a whole, the study illustrates a promising approach to conceptualizing and analyzing behavioral mechanisms of mutual behavior, an important component of an integrated study of social behavior.

Nesting microhabitat comparison of Central stoneroller and Bluehead chub: potential inference for host-switching by nest associates

Several nest-building North American minnows (Cyprinidae) function as reproductive hosts to nest associates–species that require nests of other species for spawning. Understanding the microhabitat preferences of hosts can yield insight into the reproductive ecology of many species, especially of nest associates that can utilize nests of two or more hosts. We observed nests of Central stoneroller Campostoma anomalum in which several associate species were actively spawning. Bluehead chubs Nocomis leptocephalus began constructing nests two days later in the same stream, at which time associates abandoned stoneroller nests and continued on to spawn on chub nests. This presented a unique opportunity for accomplishing two objectives: (1) quantifying stoneroller nesting microhabitat preference and (2) comparing stoneroller and chub habitat preference to gain insight into the mechanisms that may drive host switching by nest associates. We measured substrate size, current velocity, water depth, and egg depth on seven paired stoneroller and chub nests, and compared these measurements to paired microhabitat measurements at a randomly selected point near each nest. Repeated measures analysis of variance with post hoc Tukey tests revealed that stonerollers exhibited distinct nesting microhabitat preferences from chubs. Gravel on stoneroller nests was considerably smaller than on chub nests and stonerollers nested in shallower depths than chubs. However, both species nested at similar current velocities. If nest associates switch partners based on the physical characteristics of nests, then substrate size is likely the most important factor. The larger gravel sizes on chub nests likely provide better egg aeration than stoneroller nests. Chub nests may also be safer for associate broods because male Bluehead chubs cover eggs with gravel after spawning; stonerollers do not. Future work should take an experimental approach to elucidate these mechanisms.

Temporal dynamics of a commensal network of cavity-nesting vertebrates: increased diversity during an insect outbreak.

Network analysis offers insight into the structure and function of ecological communities, but little is known about how empirical networks change over time during perturbations. "Nest webs" are commensal networks that link secondary cavity-nesting vertebrates (e.g., bluebirds, ducks, and squirrels, which depend on tree cavities for nesting) with the excavators (e.g., woodpeckers) that produce cavities. In central British Columbia, Canada, Northern Flicker (Colaptes auratus) is considered a keystone excavator, providing most cavities for secondary cavity-nesters. However, roles of species in the network, and overall network architecture, are expected to vary with population fluctuations. Many excavator species increased in abundance in association with a pulse of food (adult and larval beetles) during an outbreak of mountain pine beetle (Dendroctonus ponderosae), which peaked in 2003-2004. We studied nest-web dynamics from 1998 to 2011 to determine how network architecture changed during this resource pulse. Cavity availability increased at the onset of the beetle outbreak and peaked in 2005. During and after the outbreak, secondary cavity-nesters increased their use of cavities made by five species of beetle-eating excavators, and decreased their use of flicker cavities. We found low link turnover, with 74% of links conserved from year to year. Nevertheless, the network increased in evenness and diversity of interactions, and declined slightly in nestedness and niche overlap. These patterns remained evident seven years after the beetle outbreak, suggesting a legacy effect. In contrast to previous snapshot studies of nest webs, our dynamic approach reveals how the role of each cavity producer, and thus quantitative network architecture, can vary over time. The increase in interaction diversity with the beetle outbreak adds to growing evidence that insect outbreaks can increase components of biodiversity in forest ecosystems at various temporal scales. The observed changes in (quantitative) network architecture contrast with the relatively stable (qualitative) architecture of empirical mutualistic networks that have been studied to date. However, they are consistent with recent theory on the importance of population fluctuations in driving network architecture. Our results support the view that models should allow for the possibility of rewiring (species switching partners) to avoid overestimation of secondary extinction risk.

Costs for switching partners reduce network dynamics but not cooperative behaviour.

Social networks represent the structuring of interactions between group members. Above all, many interactions are profoundly cooperative in humans and other animals. In accordance with this natural observation, theoretical work demonstrates that certain network structures favour the evolution of cooperation. Yet, recent experimental evidence suggests that static networks do not enhance cooperative behaviour in humans. By contrast, dynamic networks do foster cooperation. However, costs associated with dynamism such as time or resource investments in finding and establishing new partnerships have been neglected so far. Here, we show that human participants are much less likely to break links when costs arise for building new links. Especially, when costs were high, the network was nearly static. Surprisingly, cooperation levels in Prisoner's Dilemma games were not affected by reduced dynamism in social networks. We conclude that the mere potential to quit collaborations is sufficient in humans to reach high levels of cooperative behaviour. Effects of self-structuring processes or assortment on the network played a minor role: participants simply adjusted their cooperative behaviour in response to the threats of losing a partner or of being expelled.

Room-temperature ferroelectricity in supramolecular networks of charge-transfer complexes

Materials exhibiting a spontaneous electrical polarization that can be switched easily between antiparallel orientations are of potential value for sensors, photonics and energy-efficient memories. In this context, organic ferroelectrics are of particular interest because they promise to be lightweight, inexpensive and easily processed into devices. A recently identified family of organic ferroelectric structures is based on intermolecular charge transfer, where donor and acceptor molecules co-crystallize in an alternating fashion known as a mixed stack: in the crystalline lattice, a collective transfer of electrons from donor to acceptor molecules results in the formation of dipoles that can be realigned by an external field as molecules switch partners in the mixed stack. Although mixed stacks have been investigated extensively, only three systems are known to show ferroelectric switching, all below 71 kelvin. Here we describe supramolecular charge-transfer networks that undergo ferroelectric polarization switching with a ferroelectric Curie temperature above room temperature. These polar and switchable systems utilize a structural synergy between a hydrogen-bonded network and charge-transfer complexation of donor and acceptor molecules in a mixed stack. This supramolecular motif could help guide the development of other functional organic systems that can switch polarization under the influence of electric fields at ambient temperatures.

Romantic Relationship Status Changes and Substance Use Among 18- to 20-Year-Olds

Changes in romantic relationship status are common in emerging adulthood and may be linked to changes in substance use. This study tested the hypothesis that entry into relationships or transitioning to a more committed status leads to decreases in substance use and that dissolution of relationships or transitioning to a less committed status results in increases in substance use. Data were from a community sample of 939 individuals. Substance use (heavy drinking, marijuana use, and cigarette smoking) and relationship status (single, in a romantic relationship but not cohabiting, cohabiting, or married) were assessed at the beginning and end of three 6-month intervals between the ages of 18 and 20 years. Models were estimated to assess the association between transitions in relationship status and substance use, adjusting for prior levels of use. There were increases in heavy drinking, marijuana use, and cigarette smoking associated with dissolution of a romantic relationship, as well as increases in marijuana use and cigarette smoking associated with switching partners within a 6-month interval. Mediation analyses found some support for increases in both depressive symptoms and exposure to substance-using peers partially accounting for these associations. Decreases in substance use were not found for individuals entering into a new relationship or transitioning to a more committed relationship status. In fact, cigarette smoking increased among those who went from being single to being in a romantic relationship compared with those whose relationship status did not change. Emerging adults who experience dissolution of romantic relationships or quickly move from one relationship to another experience increased substance use. Both depressive symptoms and changes in peer environments may partially account for these changes in use.

Competition encourages cooperation: client fish receive higher-quality service when cleaner fish compete

Partner choice is likely to be an important mechanism for the maintenance of cooperation in many mutualisms, and cleaner mutualisms among fish have been a model system for testing predictions of partner choice theories. Fish seeking to be cleaned (clients) face two potential problems: cleaners may cheat them by feeding on tissue or mucous, and they may have to wait for service from a cleaner. Previous work on interactions between the bluestreak cleaner wrasse, Labroides dimidiatus, and its clients indicates that cleaners provide higher-quality service to species that have the option of switching partners. These results have been interpreted as evidence that partner choice leads cleaners to behave cooperatively; however, alternative explanations exist for these between-species patterns. Here I focus on interactions between the bluestreak cleaner wrasse and a single client species that varies in its ability to switch partners to test the prediction that clients receive higher-quality service when cleaners have to compete for access to them. The results indicate that cleaners give ornate butterflyfish, Chaetodon ornatissimus, priority of access to their services when these clients can switch partners; however, ornate butterflyfish are not cheated less often when they have access to multiple cleaner stations, and they frequently respond to cheating by aggressively chasing cleaners. In combination with previous work, these results indicate that partner choice influences cooperative interactions between bluestreak cleaner wrasse and their clients, but that some clients with the ability to switch partners may use other strategies (i.e. punishment) to limit cheating by cleaners.

Geometric stable roommates

We consider instances of the Stable Roommates problem that arise from geometric representation of participants' preferences: a participant is a point in a metric space, and his preference list is given by the sorted list of distances to the other participants. We show that contrary to the general case, the problem admits a polynomial-time solution even in the case when ties are present in the preference lists. We define the notion of an α-stable matching: the participants are willing to switch partners only for a (multiplicative) improvement of at least α. We prove that, in general, finding α-stable matchings is not easier than finding matchings that are stable in the usual sense. We show that, unlike in the general case, in a three-dimensional geometric stable roommates problem, a 2-stable matching can be found in polynomial time.

N‐terminal region of ZW10 serves not only as a determinant for localization but also as a link with dynein function

ZW10 interacts with dynamitin, a subunit of the dynein accessory complex dynactin, and functions in termination of the spindle checkpoint during mitosis and in membrane transport between the endoplasmic reticulum (ER) and Golgi apparatus during interphase. Its associations with kinetochores and ER membranes are mediated by Zwint-1 and RINT-1, respectively. A previous yeast two-hybrid study showed that the C-terminal region of ZW10 interacts with dynamitin, and part of this region has been used as an inhibitor of ZW10 function. In the present study, we reinvestigated the interaction between ZW10 and dynamitin, and showed that the N-terminal region of ZW10 is the major binding site for dynamitin and, like full-length ZW10, could potentially move along microtubules to the centrosomal area in a dynein-dynactin-dependent manner. Competitive binding experiments demonstrated that dynamitin and RINT-1 occupy the same N-terminal region of ZW10 in a mutually exclusive fashion. Consistent with this, over-expression of RINT-1 interfered with the dynein-dynactin-mediated movement of ZW10 to the centrosomal area. Given that the N-terminal region of ZW10 also interacts with Zwint-1, this region may be important for switching partners; one partner is a determinant for localization (kinetochore and ER) and the other links ZW10 to dynein function.