Colonization Of Islands Research Articles

Island colonization in flowering plants is determined by the interplay of breeding system, lifespan, floral symmetry, and arrival opportunity.

Among flowering plants, self-compatibility, longer lifespan, and generalized pollination syndrome are each thought to increase the lifetime odds of finding a mate, particularly in isolated locales. An accumulated body of evidence supports the role of breeding system in island colonization, but less is known about the impact of other traits and their interactions during establishment. We employ a global dataset of 3222 flowering plant species from 169 families to estimate the effects of traits on the probability of island occurrence. Our analyses additionally account for taxonomic group membership and assess the role of island arrival opportunity. Self-compatibility is strongly associated with island colonization. A longer lifespan and generalized pollination syndrome are also associated with increased island colonization, although this is influenced by their interaction with breeding system. The probability of island colonization is highly dependent on taxonomically conserved unmeasured traits and arrival opportunity. As expected, mate limitation appears to increase with dispersal distance, although many other factors are at play. We find that arrival opportunity and breeding system are the primary drivers of island colonization relative to other life-history traits we account for here, lending additional support for the positive role of uniparental reproduction in establishment following long-distance dispersal.

Repeated evolution on oceanic islands: comparative genomics reveals species-specific processes in birds

Understanding the interplay between genetic drift, natural selection, gene flow, and demographic history in driving phenotypic and genomic differentiation of insular populations can help us gain insight into the speciation process. Comparing patterns across different insular taxa subjected to similar selective pressures upon colonizing oceanic islands provides the opportunity to study repeated evolution and identify shared patterns in their genomic landscapes of differentiation. We selected four species of passerine birds (Common Chaffinch Fringilla coelebs/canariensis, Red-billed Chough Pyrrhocorax pyrrhocorax, House Finch Haemorhous mexicanus and Dark-eyed/island Junco Junco hyemalis/insularis) that have both mainland and insular populations. Changes in body size between island and mainland populations were consistent with the island rule. For each species, we sequenced whole genomes from mainland and insular individuals to infer their demographic history, characterize their genomic differentiation, and identify the factors shaping them. We estimated the relative (Fst) and absolute (dxy) differentiation, nucleotide diversity (π), Tajima’s D, gene density and recombination rate. We also searched for selective sweeps and chromosomal inversions along the genome. All species shared a marked reduction in effective population size (Ne) upon island colonization. We found diverse patterns of differentiated genomic regions relative to the genome average in all four species, suggesting the role of selection in island-mainland differentiation, yet the lack of congruence in the location of these regions indicates that each species evolved differently in insular environments. Our results suggest that the genomic mechanisms involved in the divergence upon island colonization—such as chromosomal inversions, and historical factors like recurrent selection—differ in each species, despite the highly conserved structure of avian genomes and the similar selective factors involved. These differences are likely influenced by factors such as genetic drift, the polygenic nature of fitness traits and the action of case-specific selective pressures.

Phylogenomics and phylogeographic model testing using convolutional neural networks reveal a history of recent admixture in the Canarian Kleinia neriifolia.

Multiple-island endemics (MIE) are considered ideal natural subjects to study patterns of island colonization that involve recent population-level genetic processes. Kleinia neriifolia is a Canarian MIE widespread across the archipelago, which exhibits a close phylogenetic relationship with species in northwest Africa and at the other side of the Sahara Desert. Here, we used target sequencing with plastid skimming (Hyb-Seq), a dense population-level sampling of K. neriifolia, and representatives of its African-southern Arabian relatives to infer phylogenetic relationships and divergence times at the species and population levels. Using population genetic techniques and machine learning (convolutional neural networks [CNNs]), we reconstructed phylogeographic relationships and patterns of genetic admixture based on a multilocus SNP nuclear dataset. Phylogenomic analysis based on the nuclear dataset identifies the northwestern African Kleinia anteuphorbium as the sister species of K. neriifolia, with divergence starting in the early Pliocene. Divergence from its sister clade, comprising species from the Horn of Africa and southern Arabia, is dated to the arid Messinian period, lending support to the climatic vicariance origin of the Rand Flora. Phylogeographic model testing with CNNs supports an initial colonization of the central island of Tenerife followed by eastward and westward migration across the archipelago, which resulted in the observed east/west phylogeographic split. Subsequent population extinctions linked to aridification events, and recolonization from Tenerife, are proposed to explain the patterns of genetic admixture in the eastern Canary Islands. We demonstrate that CNNs based on SNPs can be used to discriminate among complex scenarios of island migration and colonization.

THE ATTRACTIONS OF GUAR KEPAH ARCHAEOLOGICAL SITE, PENANG, MALAYSIA AS AN ARCHAEOLOGICAL HERITAGE TOURISM SITE

The Guar Kepah archaeological site in Penang, Malaysia, has been the focus of archaeological re search since 1860, revealing important insights into the prehistoric maritime community that inhabited the area approximately 5,000 years ago. Excavations at the site have revealed human skeletons, teeth, stone tools, and pottery, providing evidence of the community's burial traditions and material culture. The primary data collected from these excavations has facilitated the development of the site's tourism sector, with plans underway to establish the Guar Kepah Archaeological Center (GKAC). This study emphasises the importance of utilising primary data to create compelling narratives that contribute to the development of archaeological heritage tour packages. The Guar Kepah site serves as a case study for the development of archaeotourism, highlighting the need for a balance between site preservation and providing authentic experience to cultural tourists. The findings from this site have the potential to shed light on human relations with aquatic habitats, the importance of the mari ne environment in human evolution and ecology, island colonisation, and the establishment of maritime trade networks. The development of the Guar Kepah site as an archaeological heritage tourism location in northern Peninsular Malaysia demonstrates the commitment of the government and stakeholders to promoting sustainable heritage tourism in the region.

The diversity of ants in moderately isolated islands of Japan: towards understanding of factors affecting their colonisation success

ABSTRACT How species diversity is determined is an old question in community ecology but is not yet well understood. Island biotas offer opportunities to address this issue. Here, the ant fauna was studied in five moderately isolated islands of Japan and compared with those in reference regions on the nearby main islands to assess whether ants’ ecological characteristics affect their island colonisation success. Species that were more abundant in the reference regions were more frequently found on the islands, suggesting that ant communities on these islands are likely to have a nested subset structure. Species inhabiting both forests and open lands tended to occur more frequently in the study islands at least than those exclusively inhabiting forests, but this difference was not significant. In addition, nest sites and worker body size did not have significant effects on their occurrence in these islands. These results seem to suggest that the study islands as a whole offer various environments that support a variety of ant species with different ecological characteristics. It is suggested in this study that island size affects the species richness, as has often been reported.

Gone with the waves: the role of sea currents as key dispersal mechanism for Mediterranean coastal and inland plant species.

Thalassochory, the dispersal of propagules through marine currents, is a key long-distance dispersal (LDD) mechanism with implications for global biogeography and particularly for island colonization. The propagules of coastal plant species are generally assumed to be better adapted for sea dispersal than those of inland plants, but this hypothesis remains largely untested. We conducted experiments on four genera (Juniperus, Daucus, Ferula, and Pancratium) and compared traits among nine species with different habitats and distributions. Our results showed that Juniperus spp. and P. maritimum have strong thalassochorous potential within the Mediterranean Basin. Interestingly, we did not find a clear association on the thalassochorous potential of coastal versus inland species within all the tested genera, apart from P. maritimum compared withthe endemic inland P.illyricum. These findings suggest that thalassochory may be a more common dispersal mechanism than previously assumed. The apparently weak link of dispersal syndrome with species ecology broadens the possibility of dispersal by the sea also for inland plants, although considered to be poorly salt-tolerant. Moreover, our results reveal significant differences in sea dispersal between endemic and widespread species, but do not rule out an important role of thalassochory in shaping the distribution patterns of archipelago endemic flora. The presented method is largely replicable and could be used for further studies with a larger set of species to better delineate trends of sea dispersal syndrome among species with different ecology or dispersal traits.

The chronology of the human colonization of the Canary Islands

The human colonization of the Canary Islands represents the sole known expansion of Berber communities into the Atlantic Ocean and is an example of marine dispersal carried out by an African population. While this island colonization shows similarities to the populating of other islands across the world, several questions still need to be answered before this case can be included in wider debates regarding patterns of initial colonization and human settlement, human-environment interactions, and the emergence of island identities. Specifically, the chronology of the first human settlement of the Canary Islands remains disputed due to differing estimates of the timing of its first colonization. This absence of a consensus has resulted in divergent hypotheses regarding the motivations that led early settlers to migrate to the islands, e.g., ecological or demographic. Distinct motivations would imply differences in the strategies and dynamics of colonization; thus, identifying them is crucial to understanding how these populations developed in such environments. In response, the current study assembles a comprehensive dataset of the most reliable radiocarbon dates, which were used for building Bayesian models of colonization. The findings suggest that i) the Romans most likely discovered the islands around the 1st century BCE; ii) Berber groups from western North Africa first set foot on one of the islands closest to the African mainland sometime between the 1st and 3rd centuries CE; iii) Roman and Berber societies did not live simultaneously in the Canary Islands; and iv) the Berber people rapidly spread throughout the archipelago.

Phylogenetic and phylogeographic evidence for the colonization success of the diplochorous Astydamia latifolia across the Canary Islands.

Astydamia latifolia is the only species of the genus Astydamia, which forms an early-diverging lineage of Apiaceae, subfamily Apioideae. This species is subendemic to the Canary Islands and one of the most representative species of the coastal environments of this archipelago. Astydamia displays diplochory, that is, diaspores with two long-distance dispersal (LDD) syndromes. In particular, A. latifolia has both anemochorous and thalassochorous fruit traits (corky and winged mericarps). Although we expect this species to have a high dispersal capacity, there is no genetic study addressing it. The divergence time of this species from its sister taxon is also unknown. In this study, we aimed (i) to unveil the phylogenetic relationships and divergence times of A. latifolia; (ii) to reconstruct its phylogeographic structure across the Canary Islands; and (iii) to estimate the number of inter-island colonization events. To these ends, we first sequenced the internal transcribed spacer (ITS) region for A. latifolia, reconstructed the phylogenetic relationships of Astydamia and Apiaceae relatives and estimated divergence times. Then, two plastid DNA regions (psaI-aacD and psbK-trnS) were sequenced for 158 individuals (from 36 Canarian population and one NW African population) to reconstruct a haplotype network. The recently developed method Phylogeographic Analysis of Island Colonization Events (PAICE) was used to estimate the number of inter-island colonization events. Results show that A. latifolia is a phylogenetically isolated lineage that diverged from the most closely related genus (Molopospermum) in the Eocene-Miocene. It displays a low plastid DNA diversity (only four haplotypes detected), which is accompanied by a high degree of haplotype sharing between islands and highly linear rarefaction curves of colonization obtained in PAICE. These findings suggest a high colonization ability for this species, most likely related to the availability of two LDD syndromes.

Trait correlation and the assembly of island plant communities: Evidence from the Southwest Pacific

AbstractAimsPredictable and consistent differences between island and mainland organisms arising from biased colonization/establishment are known as insular assembly rules. Baker's rule is a long‐standing assembly rule predicting that the incidence of dioecy among early island colonizers should be lower than that of the mainland source pool. While Baker's rule is an established pattern of island floras, whether it results from trait correlation or factors other than insularity remains poorly understood. Here, I investigated the relative roles of insularity, climate, and dioecy‐correlated traits in regulating the incidence of dioecy across islands.LocationSouthwest Pacific.MethodsI amassed a data set of 485 plant species distributed across eight archipelagos surrounding New Zealand. Trait correlation was estimated using an association rule algorithm. I then used a null model and undirected network models to test for Baker's rule and to disentangle the relative roles of insularity, climate, and dioecy‐correlated traits in filtering dioecy among undifferentiated island colonizers.ResultsSome archipelagos conformed to Baker's rule, but the incidence of dioecy was not directly linked to insularity. Instead, it was directly regulated by dioecy‐related traits, that is, fleshy‐fruitedness and woody habit, which in turn were primarily driven by climate.ConclusionsIsland assembly rules can result from trait correlation. While results were partially consistent with predictions by Baker's rules, this resulted from dioecy‐related traits being largely excluded from island colonization/establishment because of climatic factors, not insularity. Geographic variation in this plant breeding system can be determined endogenously, rather than by being filtered directly by the characteristics of islands per se.

Integrative taxonomy of an East Asian songbird indicates rapid dwarfism after island colonization

AbstractAnimals that colonize islands often undergo significant evolutionary changes in comparison with their continental counterparts as a response to specific island conditions. The pace of such changes can be relatively fast, which poses challenges in the evaluation of the taxonomic status of island taxa. The Japanese and Manchurian Bush Warbler species complex (Horornis diphone–canturians), which breeds in East Asia and the Japanese Archipelago, is such an avian example. This species complex exhibits significant morphological differentiation between different taxa, and the taxonomic status and phylogenetic relationships within the complex are debated. Here, we updated the taxonomy of this species complex and shed insight on its evolutionary history using multi‐locus phylogeographic and acoustic analyses. Our results support the conventional treatment of the two continental taxa borealis and canturians as subspecies of H. canturians, contrary to some recent proposals that they are affiliated to H. diphone. We also document a reduction in body size, that is dwarfism, and vocal divergence in the nominate subspecies H. d. diphone, which is endemic to the remote and isolated Ogasawara Islands. These changes may have happened following colonization of these islands, which was estimated to have taken place approximately 0.2 million years ago. Although H. d. diphone is clearly distinctive and deserves recognition as an evolutionarily significant unit, H. d. diphone and other H. diphone samples were not reciprocally monophyletic. Because of this lack of reciprocal monophyly and a relatively recent divergence time, we advocate maintaining its current subspecies status. We also detected reduced genetic diversity, measured as heterozygosity, in H. d. diphone. We suggest that conservation efforts in the Ogasawara Islands should prioritize the protection of this endemic subspecies. Collectively, our findings suggest that the separation between the populations on the East Asian continent and the Japanese Archipelago, followed by colonization of remote oceanic islands through long‐distance dispersal, underlie rapid phenotypic and genetic diversification of the Horornis diphone–canturians species complex.

Consistent accumulation of transposable elements in species of the Hawaiian Tetragnatha spiny-leg adaptive radiation across the archipelago chronosequence

Abstract The ecological and phenotypic diversity observed in oceanic island radiations presents an evolutionary paradox: a high level of genetic variation is typically required for diversification, but species colonizing a new island commonly suffer from founder effects. This reduction in population size leads to lower genetic diversity, which ultimately results in a reduction in the efficiency of natural selection. Then, what is the source of genetic variation which acts as the raw material for ecological and phenotypic diversification in oceanic archipelagos? Transposable elements (TEs) are mobile genetic elements that have been linked to the generation of genetic diversity, and evidence suggests that TE activity and accumulation along the genome can result from reductions in population size. Here, we use the Hawaiian spiny-leg spider radiation (Tetragnatha) to test whether TE accumulation increases due to demographic processes associated with island colonization. We sequenced and quantified TEs in 23 individuals representing 16 species from the spiny-leg radiation and 4 individuals from its sister radiation, the Hawaiian web-building Tetragnatha. Our results show that founder effects resulting from colonization of new islands have not resulted in TE accumulation over evolutionary time. Specifically, we found no evidence for increase in abundance of specific TE superfamilies, nor an accumulation of ‘young TEs’ in lineages which have recently colonized a new island or are present in islands with active volcanoes. We also found that the DNA/hAT transposon superfamily is by far the most abundant TE superfamily in the Tetragnatha radiation. This work shows that there is no clear trend of increasing TE abundance for the spiny-leg radiation across the archipelago chronosequence, and TE accumulation is not affected by population oscillations associated with island colonization events. Therefore, despite their known role in the generation of genetic diversity, TE activity does not appear to be the mechanism explaining the evolutionary paradox of insular diversification in the Tetragnatha spiny-leg radiation.

Arrival of crocodilians to São Tomé Island, Gulf of Guinea, Western Africa, highlights the role of sea currents to the natural colonization of islands

Abstract Historical and recent arrivals of crocodilians to the Gulf of Guinean Oceanic Island of São Tomé have intrigued naturalists for several centuries. Here we present the revision of the historical records, and present data regarding the recent arrival of a single specimen in 2021. After being killed by the local authorities, the specimen was preserved and studied both through morphological and molecular methods. Our findings suggest that the specimen was a sub-adult Nile crocodile, Crocodylus niloticus Laurenti, 1768, which most likely drifted from the Congo or Ogooué river mouths in West Africa by the oceanic current acting on the Gulf of Guinea. The story of this individual highlights the dispersion paths that have contributed by the past biological colonization of São Tomé Island.

Unraveling Island Economies through Organic Residue Analysis: The Case of Mocha Island (Southern Chile)

Abstract Biophysical conditions played a fundamental role in early human colonization of insular territories, particularly in food-producing societies dealing with limited resources and the challenges of maintaining a sustainable carrying capacity. Studies on past human colonization of small oceanic islands thus offer insights into economic plasticity, ecological impacts, and adaptation of early food-producing groups. On the coast of southern Chile, early evidence is dated to 950 cal BP of island colonization by coastal populations with mainland subsistence systems based on the exploitation of marine resources, along with gathering, managing, and cultivating plants and hunting terrestrial animals. Strikingly, the extent to which these mixed economies contributed to insular colonization efforts is largely unknown. Here we used organic residue analysis of ceramic artifacts to shed light on the subsistence of populations on Mocha Island in southern Chile. We extracted and analyzed lipids from 51 pottery sherds associated with the El Vergel cultural complex that flourished in southern Chile between 950 and 400 cal BP. Chemical and stable isotope analysis of the extracts identified a range of food products, including C3 and C4 plants and marine organisms. The results reveal the central role of mixed subsistence systems in fueling the colonization of Mocha Island.

Who, Why, When, and Where From? The Peopling of the Canary Islands and the Challenges of Archaeometry

Archaeologists in the Canary Islands have gathered substantial quantitative data from radiocarbon measurements and aDNA analyses. While undeniably helpful and necessary for apprehending past human activity, their interpretation, based on theories underpinning models developed for island chains, has lagged, leaving a gap in our understanding of processes of occupation and social network systems. The decontextualized nature of the archaeological landscape of the Canaries and a lack of consensus about proper radiocarbon methodologies are some of the factors contributing to heated scholarly debate. Here, for the Canary Islands, the author reviews the current literature on aDNA and discusses settlement theories, the chronological evidence used for occupation models, and how such perspectives align with current thinking on island colonization.

The sweet tabaiba or there and back again: phylogeographical history of the Macaronesian Euphorbia balsamifera.

Biogeographical relationships between the Canary Islands and north-west Africa are often explained by oceanic dispersal and geographical proximity. Sister-group relationships between Canarian and eastern African/Arabian taxa, the 'Rand Flora' pattern, are rare among plants and have been attributed to the extinction of north-western African populations. Euphorbia balsamifera is the only representative species of this pattern that is distributed in the Canary Islands and north-west Africa; it is also one of few species present in all seven islands. Previous studies placed African populations of E. balsamifera as sister to the Canarian populations, but this relationship was based on herbarium samples with highly degraded DNA. Here, we test the extinction hypothesis by sampling new continental populations; we also expand the Canarian sampling to examine the dynamics of island colonization and diversification. Using target enrichment with genome skimming, we reconstructed phylogenetic relationships within E. balsamifera and between this species and its disjunct relatives. A single nucleotide polymorphism dataset obtained from the target sequences was used to infer population genetic diversity patterns. We used convolutional neural networks to discriminate among alternative Canary Islands colonization scenarios. The results confirmed the Rand Flora sister-group relationship between western E. balsamifera and Euphorbia adenensis in the Eritreo-Arabian region and recovered an eastern-western geographical structure among E. balsamifera Canarian populations. Convolutional neural networks supported a scenario of east-to-west island colonization, followed by population extinctions in Lanzarote and Fuerteventura and recolonization from Tenerife and Gran Canaria; a signal of admixture between the eastern island and north-west African populations was recovered. Our findings support the Surfing Syngameon Hypothesis for the colonization of the Canary Islands by E. balsamifera, but also a recent back-colonization to the continent. Populations of E. balsamifera from northwest Africa are not the remnants of an ancestral continental stock, but originated from migration events from Lanzarote and Fuerteventura. This is further evidence that oceanic archipelagos are not a sink for biodiversity, but may be a source of new genetic variability.

Digest: Islands promote population differentiation in dispersive swallows.

How can highly dispersive species give rise to genetically distinct populations? This seemingly paradoxical pattern is common among insular birds, but not in those with continental distributions. Broyles and Myers sequence the genomes of almost 150 individuals from the island-dwelling Pacific swallow (Hirundo tahitica) and its continental counterpart, the welcome swallow (H. neoxena). They find strong population structure only among island populations and attribute this to a behavioral reduction in dispersal propensity following island colonization. However, wing shape remains consistent across populations, suggesting it might not accurately reflect dispersal propensity in this group. This study illustrates the interplay between dispersal, isolation, and divergence, offering insights into how geographic factors affect speciation and population differentiation on islands.

Reconstructing the complex colonisation histories of lizards across Mediterranean archipelagos

AbstractAimThe Mediterranean Basin is a global biodiversity hotspot and has one of the longest histories of human–biota interactions. Islands host a large fraction of Mediterranean diversity and endemism, but the relative importance of natural versus human‐mediated colonisation processes in shaping the distribution and genetic structure of Mediterranean island fauna remains poorly understood. Here, we combine population genomics, demographic models and palaeoshoreline reconstructions to establish the island‐colonisation dynamics of wall lizards in Mediterranean archipelagos.LocationFour Mediterranean archipelagos in Italy and Croatia.TaxonThe wall lizard Podarcis siculus.MethodsWe used ddRAD sequencing to genotype 140 lizards from 23 island and mainland populations. Analyses of admixture and site frequency spectra were used to reconstruct population structure, demographic history and variation of gene flow through time. Genomic results were integrated with palaeogeographical reconstructions and were compared to archaeological evidence of human presence on these islands.ResultsAlthough many island populations of this species are assumed to be non‐native, we find that many islands were colonised long before any known human settlements (230,000–12,000 years ago). This natural colonisation most likely occurred through land bridges during glacial marine regression or by over‐sea rafting. On the other hand, islands distant from the continent were often colonised recently, and some of the estimated island colonisation times match historical records of human arrival. We also determine that long‐established island populations generally show lower genetic diversity compared to proximate mainland populations, contrary to recently colonised islands that must have experienced higher rates of post‐colonisation gene flow.Main ConclusionOur integrated approach provides us with the power to accurately quantify the origin, timing and mode of island colonisation. This framework helps to clarify the biogeographical and evolutionary history of island populations, with important implications for conservation and management of island biodiversity.

Evolutionarily labile dispersal behavior and discontinuous habitats enhance population differentiation in island versus continentally distributed swallows.

The causes of population divergence in vagile groups remain a paradox in evolutionary biology: dispersive species should be able to colonize new areas, a prerequisite for allopatric speciation, but dispersal also facilitates gene flow, which erodes population differentiation. Strong dispersal ability has been suggested to enhance divergence in patchy habitats and inhibit divergence in continuous landscapes, but empirical support for this hypothesis is lacking. Here we compared patterns of population divergence in a dispersive clade of swallows distributed across both patchy and continuous habitats. The Pacific Swallow (Hirundo tahitica) has an insular distribution throughout Southeast Asia and the Pacific, while its sister species, the Welcome Swallow (H. neoxena), has a continental distribution in Australia. We used whole-genome data to demonstrate strong genetic structure and limited introgression among insular populations, but not among continental populations. Demographic models show that historic changes in habitat connectivity have contributed to population structure within the clade. Swallows appear to exhibit evolutionarily labile dispersal behavior in which they reduce dispersal propensity after island colonization despite retaining strong flight ability. Our data support the hypothesis that fragmented habitats enhance population differentiation in vagile groups, and suggest that labile dispersal behavior is a key mechanism underlying this pattern.

Shell Tools and Use-Wear Analysis: a Reference Collection for Prehistoric Arabia

Prehistoric and Archaeological research has pointed out the role of marine resources in modern humans’ cognitive and cultural developments. Maritime adaptations constitute a key component of the sociocultural evolution in Eastern Arabia. During the Neolithic (c. 6500–3300 BCE), it is expressed by the colonisation of offshore islands supported by advanced seafaring and the exploitation of marine resources not only for staple food but also for obtaining hard animal materials used for both symbolic and technological productions, respectively in the form of personal adornments and tooling. Although tools made of retouched large marine mollusc shells are reported on several sites, no detailed study has been conducted on their function and role within the socio-technological processes.The present study introduces a prospective approach for the functional analysis of archaeological shell tools from Eastern Arabia. A reference collection of use-wear traces made experimentally has been built: it compiles the results of 65 experiments (23 are documented and illustrated in the present study), including the processing of various animal, vegetal, and mineral materials. Use-wear traces have been observed and described using both low and high-power magnifications (conducted mainly at 100 ×). It provides helpful methodological support for future comparisons with archaeological specimens. The procurement conditions of the shell valves and the techniques of retouch have been discussed in detail, allowing further considerations on the degree of the socio-technological investment devoted to these peculiar artefacts.

Shell Midden Archaeology: Current Trends and Future Directions

Since the 19th century, the study of shell middens has played an important role in archaeological research. Shell midden and broader coastal archaeology have transformed our understanding of human relationships with aquatic habitats, demonstrating the importance of marine environments to human evolution and ecology, the colonization of islands and establishment of maritime trade networks, changing social and political dynamics, and a variety of other issues. During the past two decades, shell midden research has greatly increased, marking an exciting time for new discoveries and heightened collaboration with Indigenous communities. Several key research trends in shell midden archaeology during the past 10–15 years include research on site distribution and temporality, underwater archaeology, historical ecology, terraforming, landscape legacies, and community collaboration. These research trends demonstrate the ways in which shell midden archaeologists are shaping our understanding of the human past and environmental change around the world.