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Behavioral plasticity within species is adaptive which directs survival traits to takemultiple pathways under varying conditions. Male–male cooperation is an evolutionarystrategy often exhibiting an array of alternatives between and within species. Africanmale lions coalesce to safeguard territories and mate acquisition. Unique to thesecoalitions is lack of strict hierarchies between partners, who have similar resourcesecurities possibly because of many mating opportunities within large female groups.Skewed mating and feeding rights have only been documented in large coalitions where maleswere related. However, smaller modal prey coupled with less simultaneous matingopportunities for male Asiatic lions in Gir forests, India would likely result in adifferent coalition structure.

Observations on mating events ( n = 127)and feeding incidents ( n = 44) were made on 11 male coalitions and 9female prides in Gir, to assess resource distribution within and among different sizedmale coalitions. Information from 39 males was used to estimate annual tenure-holdingprobabilities. Single males had smaller tenures and appropriated fewer matings thancoalition males. Pronounced dominance hierarchies were observed within coalitions, withone partner getting more than 70% of all matings and 47% more food. Competition betweencoalition partners at kills increased with decline in prey size, increase in coalitionsize and the appetite states of the males. However, immediate subordinates in coalitionshad higher reproductive fitness than single males.

Declining benefits to partners withincreasing coalition size, with individuals below the immediate subordinates havingfitness comparable to single males, suggest to an optimal coalition size of 2 lions. Lionsunder different competitive selection in Gir show behavioral plasticity to formhierarchical coalitions, wherein partners utilize resources asymmetrically, yet coalescefor personal gains. BACKGROUNDCooperation among males is an evolutionary strategy to enhance fitness of partners througha better defense of resources and reproductive opportunities.

Such a strategy has been reported indiverse mammalian species like lions Panthera leo (;;; ), cheetahs Acinonyxjubatus ,striped hyenas Hyaena hyaena , chimpanzees Pan troglodytes (;; ), howler monkeysAlouatta seniculus , baboons Papio spp. (;; ), feral horses Equuscaballus , meerkatsSuricata suricatta , coastal river otters Lutra canadensis , and bottlenose dolphinsTursiops truncatus. Yet, the degrees of cooperation among male partners vary dramaticallybetween species, from simple alliances in feral horses and coastal river otters to complex coalitions in nonhuman primates. Ethics statementAll permissions to carry out field work were obtained from the Office of the ChiefWildlife Warden (CWLW), Gujarat under the provisions of the Wildlife Protection Act, 1972(permit number: WLP/28/C/–16).

Radio-collaring of lions was approved by theMinistry of Environment, Forests and Climate Change (MoEFCC), India (permit number:22–7/2002 WL-I) and CWLW, Gujarat (permit number: WLP/26/B/356–61), and carried out underthe supervision of field veterinary officers. Gir lions are quite accustomed to people onfoot and in close proximity (; ) andbehavioral observations on the individuals were done only after prolonged acclimatizing toour presence. Such habituations allowed us to observe them from as close as 20 m withouthindering their daily behavioral repertoires. Study site and populationBetween December 2012 and December 2016, 70 adult lions (21 males and 49 females)belonging to 11 coalitions and 9 prides were studied, encompassing an area of about 1200km 2 in the western part of the Gir Protected Area (Gir PA hereafter) and itsadjoining human-dominated landscape (21°17′-20°55′N and 70°20′ - 70°52′E) in Gujarat,India. The study animals were a subset of the larger lion population in Gir PA (1800km 2) of around 250 individuals, which have been studied continuously since1995 (,;;,;; ). The intensive study areacomprised of parts of the western Wildlife Sanctuary and the central National Park, andparts of the south-western agricultural landscape which is outside the formal boundariesof the PA.

Gir PA is a dry-deciduous forest tract characterized by a semiarid climate with Tectonagrandis, Anogeissus spp., Acacia spp. AndZiziphus spp. As the dominant vegetation (;, ).The stretch outside the PA comprised mainly of farmlands, croplands, mango-orchards andProsopis spp.-Acacia spp. Selection of coalitionsMales were categorized to be in a coalition when they were frequently seen in eachother’s company, shared kills, hunted, vocalized and patrolled their territories together. Due to long-term researchand intensive monitoring system in the study area since early 1990s (;,;;, Mena 2009;;;;), many lions wereindividually identifiable along with information on their ranging patterns and lifehistories. Using this prior information, territorial male coalitions: 1) of varying sizes,and 2) with information since they became residents in the area were selected.

We chosecoalitions with neighbouring ranges as coalitions dispersed over a very large area weredifficult to monitor simultaneously with intense rigor. A total of 11 coalitionscomprising of singletons/single male ( n = 4), doubletons/2-malecoalitions ( n = 5), more than 3 male coalitions ( n = 2)and their interacting 9 female prides ( n = 49 adult females) wereselected for behavioral observations and were monitored for periods ranging between 1.5and 4 years. Identification and monitoringStudy individuals were uniquely identified using their vibrissae patterns and additionalbody marks (; ). A combination ofradio-telemetry and intensive search using cues such as pugmarks, prey-alarm calls, roars,kills, and information from tourists were used to track and monitor the individuals. Twoadult individuals (1 male belonging to a coalition of 4 males and 1 female belonging to apride of 3 adult females) were radio-collared (GPS collars, Vectronics Aerospace GmbH,Berlin, Germany, weighing less than 1% of the animal’s bodyweight).

The entire monitoringperiod of each male was divided into 2-day sampling occasions as mating observationsnecessitated each male to be visually located at least once in 2 days, so as not to missrecording a mating event (lion mating events typically range from 2 to 6 days,;; ). Such intensive monitoring was possible owing to rigorous fieldwork aidedwith an age-old practice of the forest department to track individual lions every day(;; ). Our efforts led to the detection of each male in 92 ± 1% of all thesampling occasions (Supplementary Table S1). All the study individuals were familiar toour presence, and were followed on foot or a 4-wheel drive vehicle. Mating eventsMating events were recorded by locating each study male every day or every alternateday. Upon locating a male, the GPS coordinates, surrounding habitat, state of activityand associated animals were noted.

One mating event was considered to be the entireduration when a male consorted a lioness in estrus (included the initial courting phase,actual copulations and intervals between successive copulations, see SupplementaryFigure S1 for details) till the pair parted ways and returned to their respectivegroups. Once a mating pair was found, the male and female were identified to theircoalition and pride respectively, and a continuous 24-h focal behavior sampling (Altmann1974) was done for all days the mating event lasted. Pairs were kept in view within 50 mfrom observers day and night. During dark nights a flash light was used every 15–30 minto ascertain location of the mating pairs and copulations outside visible range wereconfirmed with the distinctive loud “ yowl” that males make whileejaculating (; ). Total mating durations andpartner-switching instances were recorded. For computing mating durations, we used onlythose events ( n = 119/127) where we could observe pairs from thebeginning of the events (courting phase).

Since study coalitions differed in their totalmonitored durations (depending upon their initiation of residence/being territorial inthe area), to remove bias emanating from differential sampling efforts, number of matingevents of a male was expressed as a ratio to the number of days the male was actuallydetected in the field. Also, we attempted to locate study males once in each of thesampling occasions (2 days), but we failed to detect them in a few cases (8%). Thus,there were chances that we could have missed mating events and the above mentionedcalibration addresses this problem. For each male, calibrated mating frequency wasexpressed per year and this mating index (MI = number of mating events/number of daysdetected in field × 365 was then compared between partners and tested for differencesusing a chi-square test at an α value of 0.05. Feeding eventsFeeding behavior of coalition partners was recorded from the beginning of a feedingevent (when the males started feeding on a kill) to the full utilization of the carcass(when the males permanently left it). Data were used from only those events( n = 44) where initiation of feeding was known with certainty and ≥2males were present at the site, within 100 m of the carcass. We postulated thatcompetition at kills and hence dominance-hierarchies, if any, would depend upon: 1) preysize, 2) appetite state/hunger of the males, and 3) number of individuals sharing akill.

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Prey weights were visually estimated. Before collecting data in the field, wepracticed and compared our prey weight estimating skills by accurately weighingdifferent sized whole carcasses used for feeding trials on lions in a zoo facility. We couldaccurately estimate weights of small carcasses up to 15 kg (with an error of ± 1 kg) andmedium carcasses up to 100 kg (with an error of ± 5 kg). Visual estimates of very largecarcasses (200 kg) differed slightly among observers and hence a consensus weightbetween 2 to 3 observers was taken for such prey in the field. The appetite state ofevery male lion was recorded for each event by scoring their belly sizes following technique for African lions.Each lion was given a belly score between 1 (fully gorged) and 5 (starved) (detailed in). Information regarding the feedingsequence (males taking turns or feeding simultaneously) and aggression at kills wasdocumented. Total time spent by each male feeding on a carcass was recorded throughcontinuous 24-h monitoring of the feeding events for all days a carcass was being fedupon.

Akin to mating observations, each carcass was kept in sight and night monitoringwas done using flashlights. Feeding durations were taken as surrogates of biomassconsumption. However, lions (like other carnivores) tend to selectively feed first onthe choicest body parts of prey (visceral organs and flesh, which need very low handlingtime), and then the less digestible body parts like skin, bones, and hide, which requireconsiderably higher handling durations. Consequently, a male eating first would consume more of higherquality food in relatively less time feeding on viscera and flesh than the next oneshaving to negotiate skin, bones, and hide.

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Thus, using absolute feeding duration alonewould not account for quality and amount of consumption. To circumvent this problem, weused data (from feeding trials on wild-caught lions which mimicked free-rangingconditions, ) onconsumption rates (kg eaten/h) of lions for successive days feeding on the same carcass.Whenever male partners fed sequentially from small–medium carcasses (100 kg), the correction factorwas used for males eating after 12 h from the initiation of feeding. The disparity inconsumption between partners was then calculated as the difference in correctedfeeding time on a kill. Also, aggressive behavior between the partners on akill (a measure of competition) was categorized into 2 classes: 1) aggressiveexclusion—when the feeding male(s) thwarted the advance of at least one of his (their)partners through heightened aggression and did not allow him (them) to feed, and 2) mealsharing—mild aggression between partners (squabbles and occasional swats), but allpartners shared a kill simultaneously. Fitness quotientStaying alone or forming coalitions are alternative survival/reproductive strategies formales in social mammals, including lions (;;; ). However, in African lions, males in coalitions are more successful thansingletons, producing more number of offspring. For coalitions to evolve as a strategy: 1) coalitions should beable to secure more resources compared to singletons, and b) if dominance-hierarchies arepresent within coalitions, then subordinate members should also get higher benefits thanmales which do not form coalitions, especially if coalition partners are unrelated.

Totest this postulate, we compared reproductive fitness of singletons with those that formcoalitions. Mating eventsWe recorded 127 mating events and invested 9305 h of focal sampling for collectingobservational data. Male–female mating association lasted for an average of 72.9 ± 2.8h. Also, in only 1% (2 out of 127 events) of all the recorded mating events we foundanother female of the same pride in estrus synchronously.

When compared between partnerswithin a coalition, mating indices differed significantly (χ 2 = 41.22, df =16, P = 0.0005), with one male being consistently involved in morematings than his partner(s). Skew inthe distribution of mating events between partners was highly conserved among differentcoalitions. The partners with most matings appropriated 71.6 ± 3%, the partners withnext-highest matings had 25.3 ± 1% and the partners with least matings had 1–2% of thetotal events of their respective coalitions. Distribution of observed mating events within and between coalition males. Plotsshowing: (a) Mating index of monitored lions (annual mating frequency calibrated bythe total number of days each male was detected in the field), adjacent bars withsimilar patterns represent lions from the same coalition; and (b) Lions were rankedin a descending order of mating index within each coalition. The figure showspercent matings procured by lions within a coalition averaged for each rank acrosscoalitions. Error bars represent 95% CIs.

Feeding eventsData from feeding events of free-ranging lion coalitions revealed a similar trend asfound from mating observations. Biomass consumption was highly skewed (difference inconsumption between partners 0, one-tailed t = 6.06, df = 43,P 9 (Supplementary Table S2). Fitness quotientSingletons held territories for shorter durations (annual tenure holding probability =0.47 ± 0.19) than males in coalitions. Coalitions of 2 males and more than 2 males hadsimilar annual tenure-holding probabilities (0.85 ± 0.05 and 0.81 ± 0.07, respectively).Singletons had far lower fitness quotients than subordinate males in a coalition of 2. However, in coalitions with more than 2males, the males at the bottommost ranks (rank 3 and below) had fitness comparable to thatof singletons, indicating that they would do equally good ( or poorly) ifthey remained alone. DISCUSSIONFunctional responses of behavior to different drivers of selection are crucial forindividual fitness.

Plasticity in strategies aid individuals in coping with varyingenvironmental conditions.Male cooperation to form coalitions is one such strategy which exhibits a wide array ofinter- and intraspecific variation in mammals. Coalition formation can vary within speciesdepending upon habitat and resource heterogeneity. Using lions as model species, we demonstrate behavioralplasticity to be a possible function of resource availability. Male African lions in theSerengeti system have been found to cooperate amongst themselves to gain access to food andmates, but are not reported to form strict dominance hierarchies (; Bertram 1975;;;Packer et al.1988). Asiatic lions, living in more forested habitats with smaller modal preyand less simultaneous mating opportunities, likely face selective pressures that results inpronounced dominance hierarchies within male coalitions.Our results indicate that in male Asiatic lions mate and food sharing between coalitionpartners were highly skewed. One of the males in every coalition was consistently involvedin more matings and the same individual got the lion’s share from killscompared to his partner(s). As postulated, competition at kills was high amongst partners,very prominent at small carcasses, with high appetite state of the dominant males and morepartners in a coalition.

A distinct feeding order was observed among the partners, wherethey took turns to eat from relatively smaller carcasses. The reproductively dominant malesinvariably had the first rights to carcasses, even if they were not the killers or firstpossessors. However, dominant partners were observed to share small kills amicably withtheir partners when the former had their bellies full (Supplementary Figure S3).

We alsorecorded 3 instances of intra-coalition mate switching where the female switched from onemale to its coalition partner within the same estrous duration. In all of the 3 cases theswitch happened in favor of the male who also appropriated the maximum mating opportunitiesand food at kills within that coalition. Reproductive dominance across different rankedindividuals within coalitions was found to be highly preserved among coalitions, with malesat the bottommost ranks hardly getting any matings.

Thus, in an Asiatic system, individuals in large coalitions (3–4 males) havevery asymmetrical resource securities, which might be a plausible explanation of suchcoalitions being rare. Our results primarily indicate that although male coalitions exhibitpronounced hierarchies, immediate subordinates are better off (higher fitness) thansingle-males. We predict an optimum coalition size of 2 in male Asiatic lions, below andbeyond which reproductive success of single males and low-ranking subordinates respectivelyare low. This is in accord with the ground reality of an average adult male group size of2.1 ± 0.3 in Gir. Our resultsfurther corroborate the findings of where African and Asian elephant groups ( Loxodonta africanaand Elephas maximus) show different hierarchical systems shaped by resourcecompetition, and where malealliances of bottlenose dolphins exhibit considerable variation in habitats differing inresources and threats.However, apparent reproductive fitness alone cannot explain coalition strength since inlarge coalitions (2 males) lowermost ranked individuals had very low reproductivefitness, yet such coalitions exist.

Other than mate and territory acquisitions, a coalitionmay also provide other direct benefits through group protection and food procurement. Thesemay be vital for subordinate lions for survival, gaining vigor and subsequently attempt toeither go up on the dominance ladder in the same coalition or join/form other coalitions, asreported in feral horses. We haveobserved lions that have lost their coalition partners join other males to form newcoalitions, sometimes differing widely in their ages. In African lions different agedcoalition partners were mostly found in small coalitions and large coalitions were typicallycomposed of similar aged closely related kins. Thus, genetic analysis of relatedness within different male Asiatic lioncoalitions would shed more light on the underlying mechanisms of the observed patterns.Uniqueness of the observed social structure make Asiatic lions stand out as a distinctbehavioral ecotype, highlighting plasticity of social behavior within species facingdifferent selective pressures. Record land tenure system of lions in Kruger to be similar to that found inthe Asiatic system wherein males primarily safeguard territories which encompass one-to-manyfemale prides.

It would be interesting to see if a social structure similar to what wereport for male Asiatic lions exists in Kruger and other lion systems of Africa whereforested settings make males interact less with females with the latter living in smallergroups compared to that found in the East African plains. The authors thank the Ministry of Environment Forests & Climate Change, India, ChiefWildlife Warden, Gujarat State and Chief Conservator of Forests, Junagadh for grantingpermissions and facilitation of the study.

Sandeep Kumar, Anshuman Sharma and Ram RatanNala, Deputy Conservators of Forests, Gir are deeply acknowledged for facilitating fieldwork and data collection. Sutirtha Dutta, Vishnupriya Kolipakam, and Ayan Sadhu areacknowledged for their help with data analyses. The authors thank our field assistants: LateTaj Mhd.

Bloch, Osman Ali Mhd., Ismail Umar Siraj, Hamal Heptan, Hanif Pir Mhd., Mhd.Sameer, and Iqbal Hamal Bloch for their hard-work and skill in working with lions. Withoutthem this study would not have been possible. The authors also thank the wildlife guards andtrackers of Gir Management Unit for their dedicated lion searches and information sharing.The authors thank Louise Barrett and 2 anonymous reviewers for their constructive commentson an earlier version of the manuscript. Author sequence is in order of their contributionto the research. Conceived the study; S.C. Collected field data with activeinputs from Y.V.J.; S.C.

Analyzed the data and wrote the manuscript.Data accessibility: Analyses reported in this article can be reproduced using the dataprovided.