Behavioral ecology of odometric memories in desert ants: acquisition, retention, and integration

Assuming that the acquisition and retention of memories have costs, properties of memories should fit the functional requirements for the system of memory. Based on a functional analysis of what path integration is meant to do, we predicted that odometric memories in desert ants should show (1) little improvement with repeated training: performance should be as good after one training trial as after six training trials, (2) decay of memory after 24 h, and (3) performance based solely on the most recent outbound trip, with no integration over multiple memories. Desert ants (Cataglyphis fortis) traveled in narrow straight plastic channels to forage for cookie crumbs in a feeder at 6- or 12-m distance. Each ant was tested once by being taken from the feeder and released 2 m from the end of a 32-m channel to run home. The distance at which the ant first turned back (first turn) constituted the data. In acquisition, groups trained one or six times before being tested had unsystematic scatter that did not differ significantly. In retention, ants tested after a 24-h delay showed larger unsystematic scatter than control animals tested after no delay. In integration, ants were trained five times at 6 or 12 m and then tested at 12 or 6 m, respectively. No evidence of integration of multiple odometric memories was found. The results show that the properties of odometric memories are indeed tailored to what the memory system is used fo

Wnt3a induces neuronal differentiation and crosstalk between Wnt/Ca2+-pathway and Wnt/β-catenin pathway

HumanNPCs (hNPCs) are the suitable cell source in translation medicine for neurodegenerative disease. In the present study, effects of Wnt3a on the differentiation of hNPC were studied. The results showed that Wnt3a induces canonical and non canonical Wnt pathways. Furthermore, Wnt3a increases Ca2+ target genes CaMKII and Pyk2 in the differentiating VM cells. The results demonstrated that Pyk2 decreases GSK3β activity and stabilizes β-catenin, suggesting there is an intercross between Wnt/β-catenin and Wnt/Ca2+-pathway via Pyk2

Homing abilities of the Australian intertidal ant Polyrhachis sokolova

The pressure of returning to and locating the nest after a successful foraging trip is immense in ants. To find their way back home, ants use a number of different strategies (e.g. path integration, trail following) and rely on a range of cues (e.g. patt

Head roll stabilisation in the nocturnal bull ant Myrmecia pyriformis: implications for visual navigation

Ant foragers are known to memorise visual scenes that allow them to repeatedly travel along idiosyncratic routes and to return to specific places. Guidance is provided by a comparison between visual memories and current views, which critically depends on how well the attitude of the visual system is controlled. Here we show that nocturnal bull ants stabilise their head to varying degrees against locomotion-induced body roll movements and this ability decreases as light levels fall. There are always un-compensated head roll oscillations that match the frequency of the stride-cycle. Head roll stabilisation involves both visual and non-visual cues as ants compensate for body roll in complete darkness and also respond with head roll movements when confronted with visual pattern oscillations. We show that imperfect head roll control degrades navigation-relevant visual information and discuss ways in which navigating ants may deal with this problem

Navigational Efficiency of Nocturnal Myrmecia Ants Suffers at Low Light Levels

Insects face the challenge of navigating to specific goals in both bright sun-lit and dim-lit environments. Both diurnal and nocturnal insects use quite similar navigation strategies. This is despite the signal-to-noise ratio of the navigational cues being poor at low light conditions. To better understand the evolution of nocturnal life, we investigated the navigational efficiency of a nocturnal ant, Myrmecia pyriformis, at different light levels. Workers of M. pyriformis leave the nest individually in a narrow light-window in the evening twilight to forage on nest-specific Eucalyptus trees. The majority of foragers return to the nest in the morning twilight, while few attempt to return to the nest throughout the night. We found that as light levels dropped, ants paused for longer, walked more slowly, the success in finding the nest reduced and their paths became less straight. We found that in both bright and dark conditions ants relied predominantly on visual landmark information for navigation and that landmark guidance became less reliable at low light conditions. It is perhaps due to the poor navigational efficiency at low light levels that the majority of foragers restrict navigational tasks to the twilight periods, where sufficient navigational information is still available.AN acknowledges funding support from the Australian Research Council’s (ARC) Centres of Excellence Scheme, ARC Discovery Project and Australian Postdoctoral Fellowship (DP0986606), ARC Discovery Early Career Award (DE120100019), Hermon Slade Foundation and The Defence Science and Technology Organization. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Integrated assessment of climate change adaptation options for water resources management using participatory and hydrological modelling approaches

Climate change adaptation (CCA) is a vital strategy for river basin water management which binds together environmental, agricultural and human water requirements in an uncertain future climate. Policy makers face a difficult task balancing demand and supply for conflicting water requirements, especially to justify present day economic costs for future benefits, like in CCA. No-regret adaptation options, applicable in both, current and future uncertain conditions, provide a way of dealing with these issues. However, determination of such options needs to be based on an integrated assessment of hydrologic, environmental, social, economic and institutional characteristics to be suitable in the future. Here, a three step process for determining no- regret options is presented, having been applied to the Kangsabati River basin in India. Firstly a participatory approach is used to identify potential CCA options, followed by a Multi Criteria Analysis (MCA) to determine the no- regret and suitability characteristics for the region. This approach was replicated at three levels; community, district and state (sub-national), targeting different stakeholders. Finally, hydrological modeling using Water Evaluation And Planning (WEAP) model, of the high ranking adaptation options show the expected efficacy in hydrologic terms. MCA generated no-regret options show importance of currently promoted soil and water conservation measures, like afforestation and check dams and the need for future focus on cropping pattern change. Evaluation criteria important to different stakeholders were also determined in the process, a valuable by-product useful for future water management. Present and future scenario based modelling of CCA options provides comparability in terms of suitability, scale of impacts and costs. Such assessments can be valuable tool-set for policymakers to make evidence based decisions on choice of adaptation measures and their spatio- temporal applications to improve water availability in an uncertain climate

The choreography of learning walks in the Australian jack jumper ant Myrmecia croslandi

We provide a detailed analysis of the learning walks performed by Myrmecia croslandi ants at the nest during which they acquire visual information on its location. Most learning walks of 12 individually marked naïve ants took place in the morning with a narrow time window separating the first two learning walks, which most often occurred on the same day. Naïve ants performed between 2 to 7 walks over up to 4 consecutive days before heading out to forage. On subsequent walks naïve ants tend to explore the area around the nest in new compass directions. During learning walks ants move along arcs around the nest while performing oscillating scanning movements. In a regular temporal sequence, the ants’ gaze oscillates between the nest direction and the direction pointing away from the nest. Ants thus experience a sequence of views roughly across the nest and away from the nest from systematically spaced vantage points around the nest. We show further that ants leaving the nest for a foraging trip often walk in an arc around the nest on the opposite side to the intended foraging direction, performing a scanning routine indistinguishable from that of a learning walk. These partial learning walks are triggered by disturbance around the nest and may help returning ants with reorienting when overshooting the nest, which they frequently do. We discuss what is known about learning walks in different ant species and their adaptive significance for acquiring robust navigational memories

Ocellar structure is driven by the mode of locomotion and activity time in Myrmecia ants

Insects have exquisitely adapted their compound eyes to suit the ambient light intensity in the different temporal niches they occupy. In addition to the compound eye, most flying insects have simple eyes known as ocelli, which assist in flight stabilisation, horizon detection and orientation. Among ants, typically the flying alates have ocelli while the pedestrian workers lack this structure. The Australian ant genus Myrmecia is one of the few ant genera in which both workers and alates have three ocellar lenses. Here, we studied the variation in the ocellar structure in four sympatric species of Myrmecia that are active at different times of the day. In addition, we took advantage of the walking and flying modes of locomotion in workers and males, respectively, to ask whether the type of movement influences the ocellar structure. We found that ants active in dim light had larger ocellar lenses and wider rhabdoms compared with those in bright-light conditions. In the ocellar rhabdoms of workers active in dim-light habitats, typically each retinula cell contributed microvilli in more than one direction, probably destroying polarisation sensitivity. The organisation of the ocellar retina in the day-active workers and the males suggests that in these animals some cells are sensitive to the pattern of polarised skylight. We found that the night-flying males had a tapetum that reflects light back to the rhabdom, increasing their optical sensitivity. We discuss the possible functions of ocelli to suit the different modes of locomotion and the discrete temporal niches that animals occupy.The project was supported by The Hermon Slade Foundation (HSF17/08) and the Australian Research Council through a Future Fellowship (FT140100221) and a Discovery Project grant (DP150101172