More than meets the eye: The barrier effect of the Yangtze River outflow

Abstract

The Yangtze (Changjiang) River enters the East China Sea with huge annual freshwater and sediment deposits. This outflow, known as the Changjiang diluted water (CDW), causes striking ecological gradients that potentially shape coastal species' distribution and differentiation. The CDW has long been rendered as a marine biogeographic boundary separating cold-temperature and warm-water faunas, but it remains unclear whether and to what extent it acts as an intraspecific barrier. Here, we synthesize published phylogeographic studies related to the CDW to address these issues. We find that the influence of the CDW on population differentiation is taxonomically variable, and even congeneric species may respond differently. In studies that claim the CDW is a phylogeographic barrier, the underlying assumptions explaining observed genetic breaks are sometimes incorrect, and some may have misinterpreted results due to conceptual confusion or insufficient geographic sampling. After excluding these studies, the remaining ones generally show shallow genetic divergence but significant population structure for coastal species across the CDW, suggesting that the CDW has not been a historically persistent barrier, but rather has acted as a filter within some species recently, probably after the last glacial maximum.

Life-history features and oceanography drive phylogeographic patterns of the chitonAcanthochitonacf.rubrolineata(Lischke, 1873) in the northwestern Pacific

“…Note that, as inferred from the MIGRATE-N results, this barrier effect may be weak for the directions from China to both Korea and Japan. Similar population structuring resulting from hydrographic patterns has also been reported in other marine species in the NWP (Ni et al, 2017) and other ocean systems, including the snakeskin chiton Sypharochiton pelliserpentis in New Zealand (Veale & Lavery, 2011) and coral reef fishes in the Caribbean (Taylor & Hellberg, 2006).…”

“…However, most of these studies have focused on cryptic lineages promoted by separation of marginal seas during the Pleistocene (e.g., Liu et al, 2011 ; Qiu et al, 2016 ; Wang et al, 2017 ; Xu et al, 2009 ), leaving the effects of some other biotic and/or abiotic factors largely unexplored ( Ni et al, 2015b ). Oceanographic features, habitat discontinuity, and species-specific life history can also contribute to shaping population genetic structure and patterns in various marine species ( Dong et al, 2012 ; Ni et al, 2017 ).…”

Molecular and Fitness Data Reveal Local Adaptation of Southern and Northern Estuarine Oysters (Crassostrea ariakensis)

“…The molecular data indicate that biogeographic barriers, such as the Yangtze River estuary, exist and isolate the northern and southern C. ariakensis populations. The Yangtze River estuary is known to be a notable barrier for the distribution of many marine invertebrates with lower gene flow, such as two oyster congeners of C. gigas and C. angulata (Xu, 1997;Li et al, 2017), an interpopulation of limpet (Cellana toreuma) (Dong et al, 2012) and the bivalve Cyclina sinensis (Ni et al, 2012(Ni et al, , 2017. Even marine species exhibiting high gene flow with high mobility or a long-term larval stage showed a distinctive genetic structure between the northern and southern coasts of the Yangtze River (Xu et al, 2009;Xiao et al, 2016).…”

“…In China, the Yangtze (Chang Jiang) River has long been rendered as a marine biogeographic boundary causing distinct ecological gradients, especially for temperature and salinity, and shaping adaptive differentiations in warm-tolerant and coldwater populations or species of coastal animals under spatially varying selection. Ni et al (2017) comprehensively summarized the effects of the Yangtze River as well as its interaction with coastal currents on the genetic diversity of many marine species, such as fishes, crabs, mollusks, etc., Most of the marine species exhibited divergent genetic structures between the northern and southern populations separated by the Yangtze River, while coastal currents facilitate internal gene flows within the northern or southern populations (Xu et al, 2009;Xiao et al, 2016;. These findings highlight the significant role of stochastic geographic isolation following environmental selection in ecological, evolutionary, and taxonomic studies.…”

Long-term sky islands generate highly divergent lineages of a narrowly distributed stream salamander (Pachyhynobius shangchengensis) in mid-latitude mountains of East Asia

“…During the last million years, climatic oscillations, such as the glacial expansions and retreats, may have led to current patterns of species distributions and inter-population gene flow [6–8]. Hydrological histories might change dramatically under the influence of climatic oscillations and geological changes, which can influence the phylogeographic patterns drastically by the barrier effect, especially for aquatic organisms [9, 10]. In addition, during the Quaternary period, severe climatic oscillations made a profound impact on the phylogeography of species at mid-latitudes, especially for those endemic to mountainous areas [11, 12].…”