Caught between two worlds: genes and environment influence behaviour of plains × Grevy's zebra hybrids in central Kenya

Abstract

Purpose/Objective: New definitions for some dosimetric parameters for use in quality assurance of flattening filter free (FFF) beams generated by medical linear accelerators have been suggested. The present study aims to validate these suggestions and to propose possible reference levels. Materials and Methods:The main characteristics of FFF photon beams were described in terms of: field size, penumbra, unflatness, slope and peak-position parameters. Data were collected for 6 and 10 MV-FFF beams from three different Varian TrueBeam linacs, and a Varian Clinac iX upgraded to FFF capability for its 6 MV. Measurements were performed with a 2D-array (Starcheck system from PTW-Freiburg), with a linear array (LA48 system from PTW-Freiburg) and with the portal dosimetry method GLAaS utilizing the build-in portal imager of TrueBeam.Results: All the parameters suggested to characterize the FFF beams were measured and evaluated Little variation was observed among the different linacs. Referring to two reference field sizes of 10x10 and 20x20cm 2 , at SDD=100cm and d=d max , from the portal imaging data converted into dose map with the GLAaS method, the following results were obtained, averaged on X and Y profiles. Field size: 9.95±0.02 cm and 19.98±0.03 cm (including allenergies. Penumbra: 2.7±0.3 mm and 2.9±0.3 mm for 6MV-FFF; 3.1±0.2 mmand 3.3±0.3 for 10MV-FFF. Unflatness: 1.11±0.01 and 1.25±0.01 for 6MV-FFF; 1.21±0.01 and1.50±0.01 for 10MV-FFF. Slope: 0.320±0.020 %/mm and 0.43±0.015 %/mm for 6MV-FFF; 0.657±0.023%/mm and 0.795±0.017 %/mm for 10MV-FFF. Peak Position: -0.2±0.2 mm and -0.4±0.2 mm for 6MV-FFF; -0.3±0.2 mm and 0.7±0.3 mmfor 10MV-FFF. Results would depend upon measurement depth. With thresholds set to at least 95% confidence level from the measured data, and to account for possible variations between detectors and methods and experimental settings, a tolerance set of: 1 mm for field size and penumbra, 0.04 for unflatness, 0.1 %/mm for slope and 1 mm for peak position could be proposed from our data. Conclusions:The parameters proposed to characterize the FFF profiles (in particular the unflatness, the slope and the peak position) appear to be a viable solution for routine checks, also presenting strong similarity to the conventional parameters used for flattened beams. The results from three different TrueBeams and a Clinac-iX suggested the robustness of the methods and the possibility to use general tolerances for the parameters. The data suggested also the reproducibility of beam characteristics among different systems (of the same vendor) and could therefore be possibly generalized.Purpose/Objective: A new method for IMRT verification with EBT3 has been developed, avoiding the need of a previous calibration. Performing a single scan gives the possibility to obtain results in less than one hour and avoids environmental and interscan variability. We have developed a method to evaluate measurements of two-dimensional dose distributions following the protocol described by Lewis et al, without the need of a prev...

Physiology modulates social flexibility and collective behaviour in equids and other large ungulates

“…Because all hybrids were born to plains zebra mothers, all were raised exclusively within plains zebra social groups. Behavioural observations of the individual hybrids-10 females and 15 males-showed that individuals of both sexes performed 'compromised' versions of some key social behaviours, pointing to the heritable (though not simply 'fixed') nature of behavioural traits that differentiate Grevy's-and plains-like social systems [52]. Hybrid females in plains zebra harems were more vigilant than their plains zebra counterparts, mirroring the behaviour of their more vigilant Grevy's zebra relatives.…”

“…Under purely natural conditions, Grevy's and plains zebras are not expected to mate-the ranges of the two species have overlapped at the southern edge of the Grevy's range for centuries without interbreeding. However such hybridization has recently been described [51,52] on the Ol Pejeta Reserve in Laikipia, Central Kenya, where interactions between a large (approx. 5000 member) resident plains zebra population and a small, heavily male-biased population of translocated Grevy's zebras (nine males and four females at the time of introduction to the reserve in the 1980s) produced 25 male and female F 1 hybrids, all of them sired by Grevy's males on plains females.…”

“…Either strategy involved frequent shifting among individuals and groups and thus limited the feasibility of the hybrids' more plains-like behaviour, since the formation of stable harem bonds is essential to success as a stallion. While hybrid males did occasionally take over harems of females, they were never sighted as long-term bonded stallions on more than a few contiguous occasions, suggesting they did not possess the full suite of behaviours necessary to occupy the role of a long-term social dominant in a plains zebra social structure even when life history (being raised within a plains zebra harem) and ecological context (a mesic habitat, and access to only plains-like, harem-based mating opportunities) would support this behaviour [52]. Thus, while the Grevy's  plains hybrids possessed an equal share of plains zebra genes, were raised in exclusively plains zebra social groups, and matured in an almost homogeneous plains zebra social environment, they nevertheless retained persistent behavioural traits apparently inherited from their rstb.royalsocietypublishing.org Phil.…”

A narrow window for geographic cline analysis using genomic data: Effects of age, drift, and migration on error rates

“…Mark-recapture studies on the biological inspiration for this model, swordtail fish in mountain streams, show hybrid deme sizes of <1000 adult individuals (Culumber et al, 2014). The Grevy's zebra in northern Kenya and Ethiopia has a global population size of 3000 individuals, has formed a hybrid zone with the plains zebra in an area of sympatry (Cordingley et al, 2009), only 25 individuals have been identified as hybrids (Schieltz & Rubenstein, 2015). While we cannot simulate hybrid zones on the scale of the broad mouse hybrid zone in central Europe (Janousek et al, 2012), our deme sizes are at the upper range of previous literature on cline theory (Table S2).…”

The ontogeny of occipital bone convexity in a longitudinal sample of extant humans

“…hybrids remaining longer in natal groups than is typical of either parent species (Schieltz and Rubenstein, 2015). Therefore, we should not expect Neandertal/modern human hybrids to manifest as purely intermediate between the two parent groups.…”